Connecting Organic and Physical Chemistry Students with Raman

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Chapter 3

Connecting Organic and Physical Chemistry Students with Raman Spectroscopy Eric R. Hantz, Matthew D. Sonntag, and Christian S. Hamann* Department of Chemistry & Biochemistry, Albright College, N. 13th and Bern Streets, Reading, Pennsylvania 19604, United States *E-mail: [email protected].

The profile of Raman spectroscopy may be elevated in the undergraduate chemistry curriculum by intentionally tying together students’ experiences in the organic and physical chemistry laboratories. In this way the valuable role Raman spectroscopy can play in structure elucidation is highlighted. The Committee on Professional Training of the American Chemical Society includes the category of optical molecular spectroscopy (e.g., IR, UV-Vis, Raman, and fluorescence spectroscopies) as an option in the panel of instruments required for certification. To the authors’ knowledge there are no Raman spectroscopy experiments that build directly on the analysis of compounds synthesized by students in a prior course for the intended purpose of scaffolding the curriculum. This chapter highlights the roles Raman spectroscopy may play in the determination of molecular structure when used in conjunction with other, more common techniques. Indeed, direct comparison to infrared spectroscopy holds the potential to reinforce that technique and its applications while introducing the study of Raman spectra. A set of three reaction products from electrophilic aromatic substitution, Diels-Alder, and aldol condensation (this including site-specific deuteration) is explored. All of these reactions are currently part of the organic chemistry curriculum. By combining analyses performed in organic chemistry with new laboratories written for the physical chemistry laboratory the authors hope to impress upon undergraduates the value of Raman spectroscopy in a context

© 2018 American Chemical Society Sonntag; Raman Spectroscopy in the Undergraduate Curriculum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

that builds on their previous experiences with other molecular spectroscopy methods.

Introduction Since its inception scientists have used Raman spectroscopy to investigate a wide range of chemical phenomena. The earliest report in the Journal of the American Chemical Society focused on Raman data was in 1930, shortly after the phenomenon described by Sir Chandrasekhara Venkata Raman was published (1–3). In that paper, Villars reported the Raman spectrum of dioxane, a solvent used in the study of synthetic resins (4). The author reports the spectrum as both a new finding and as a public service although the paper lacks a theoretical framework or an analysis of structure-function relationships. Of course, this work was done in a different age. The instrument used by Villars was built by co-workers at the Research Laboratory of the General Electric Company. The spectrum required “exposures of about six hours ...” (5). Fast-forward to the last 20 years: affordable, low-maintenance benchtop Raman spectroscopy instruments supported by personal computers connected to the Cloud that can record spectra in vanishingly small periods of time have facilitated both the ability to collect Raman data and the ability to distribute it widely. There has been an explosion in the number of research papers demonstrating the singular utility of Raman spectroscopy applied to a wide range of problems, enhanced and supported by computational techniques. A coordinate increase in articles published in the Journal of Chemical Education has been noted in the Introduction to this Volume (6). These factors taken together constitute a mandate for those teaching chemistry in the post-secondary environment: Faculty are being called to intentionally incorporate Raman spectroscopy into the undergraduate teaching and research curriculum, to generate authentic and relevant assignments and exercises aimed at teaching the theory and practice of this technique. But where does one begin to heed this call, especially when one (CSH) is not necessarily a Raman spectroscopist? For the examples presented in this chapter the inspiration to answer that question came from three sources: (1) a colleague whose research focuses on the use of Raman spectroscopy for the analysis of materials (MDS); (b) a re-evaluation of existing curricular goals in the department to determine what synergies could be generated from current practice (CSH); and (c) an ongoing commitment to research and curriculum development involving undergraduates (ERH). The Department of Chemistry & Biochemistry at Albright College recently hired a physical chemistry professor (MDS) whose research profile included Raman spectroscopy. In support of his work the College purchased the appropriate Raman instrument plus chemicals and ancillary laboratory equipment so he and his research, laboratory development, and course-based laboratory students could study the practice of Raman spectroscopy in the physical chemistry curriculum. To provide context for this hire, note that the Department offers degrees in chemistry and biochemistry that are certified by the American Chemical Society (ACS). Currently there are approximately 70 majors and co-majors distributed 36 Sonntag; Raman Spectroscopy in the Undergraduate Curriculum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

over the 4-year curriculum. A 5-year running average indicates 6 chemistry and 12 biochemistry majors graduate per year; 30% go to graduate school and 20% go to medical school (7). Overall, the College has approximately 1,800 undergraduate students and a small master’s program in education. The chemistry and biochemistry curricula have in common 2 semesters of general analytical chemistry in the first year and 2 semesters of organic chemistry in the second year. Chemistry majors take 2 semesters of physical chemistry in the third year; biochemistry majors take 2 semesters of biochemistry in the third year and have the option of taking the 2-semester physical chemistry sequence in the third or the fourth year. All of these courses have an associated laboratory component. The physical chemistry course has the potential to include both lecture and laboratory components focusing on Raman spectroscopy. These exercises allow students to study both the theory and the practice of this technique and to place them in the broader context of optical molecular spectroscopy, an area of study on the list of options provided by the Committee on Professional Training that are required for ACS certification (8). There are three other spectroscopies that meet the optical molecular spectroscopy category: infrared (IR), fluorescence, and ultraviolet-visible (UV-Vis) (9). At the College, fluorescence and UV-Vis are introduced in the general analytical courses and IR is introduced in the organic chemistry courses. These four courses taken together are designed to set the stage for upper-level courses as well as laboratory development and undergraduate research experiences. In each case, the spectroscopy technique is introduced in authentic ways with as much hands-on time as is practicable. (Nuclear magnetic resonance spectroscopy is introduced in the organic chemistry courses (10).) Note that IR is revisited in physical chemistry; fluorescence is revisited in physical chemistry and biochemistry; and UV-Vis is revisited in every subsequent course. This curricular scaffolding is not uncommon and indeed provided some of the inspiration for the work described in this chapter (11). Specifically, since Raman spectroscopy is most obviously related to IR spectroscopy it made intuitive sense to introduce it into the organic chemistry sequence so that by the time students arrived in physical chemistry they had some idea of what Raman spectroscopy is used for and had some experience with the instrument. Of course, one does not want to overload the content of any one course. In the examples described herein, this does not seem to be a problem – indeed, the introduction of Raman spectroscopy in the organic chemistry sequence increases the opportunities for students not only to learn something about Raman spectroscopy but also to more deeply appreciate IR spectroscopy. Thus, a review of the organic chemistry laboratory curriculum was engaged with the goal of finding appropriate experiments in which to introduce Raman spectroscopy. Once it is determined where in the laboratory sequence the technique would be introduced, the appropriate place to introduce the technique in lecture would be known because the lecture and laboratory curricula are intentionally correlated. Currently, NMR (12) and IR spectroscopy along with mass spectrometry are introduced in the fall semester. In this way students can use these techniques more frequently as they engage in experiments focused on carbon-carbon bond formation. Also currently, these experiments include 37 Sonntag; Raman Spectroscopy in the Undergraduate Curriculum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

electrophilic aromatic substitution (13, 14), the Diels-Alder reaction (15), and the aldol condensation (16).

Distinguishing Regioisomers in an Electrophilic Aromatic Substitution Reaction Students engage an electrophilic aromatic substitution reaction in which they alkylate 1,4-dimethoxybenzene with a series of alcohols under acidic conditions (13, 14). An example of this reaction is shown in Figure 1. Spectroscopic characterization includes 1H NMR, 13C NMR, and IR spectroscopies as well as mass spectrometry. While the student learning outcomes for this experiment have been satisfactory over the years, due to the symmetry of the product molecule students are unable to rigorously exclude the synthesis of 2,3-di-tert-butyl-1,4-dimethoxybenzene based on NMR spectroscopy alone (Figure 2). (Note that 2,6-di-tert-butyl-1,4-dimethoxybenzene can be excluded because it would have 4 aromatic signals in the 13C NMR spectrum.)

Figure 1. The dialkylation of 1,4-dimethoxybenzene with tert-butanol (tBuOH) using H2SO4 (sulfuric acid) as catalyst and acetic acid as solvent yields 2,5-di-tert-butyl-1,4-dimethoxybenzene.

Figure 2. Both 2,5-di-tert-butyl-1,4-dimethoxybenzene (left) and 2,3-di-tert-butyl-1,4-dimethoxybenzene (right) would have 3 signals in the aromatic region of their respective 13C NMR spectra. 2,6-Di-tert-butyl-1,4-dimethoxybenzene (middle) would have 4 aromatic signals. For the purposes of the second-year organic chemistry curriculum students are allowed to use the argument that “this product is unlikely due to steric hindrance” but in the absence of an authentic sample only x-ray crystallography can unambiguously identify which regioisomer students actually synthesize (17). Can Raman spectroscopy provide a more satisfying answer to this question? 38 Sonntag; Raman Spectroscopy in the Undergraduate Curriculum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

Comparison of the IR and Raman spectra of 2,5-di-tert-butyl-1,4dimethoxybenzene provides a tantalizing suggestion that Raman spectroscopy might indeed be able to distinguish the two possible regioisomers that NMR spectroscopy cannot (Figure 3) (18). Even if in the absence of an authentic sample of both compounds it cannot, Raman spectroscopy does provide a satisfying comparison to IR spectroscopy and thus is worthy of inclusion at this point in the curriculum. Several features in Figure 3 illustrate this point. A foundational physical principle for IR absorption is that the intensity of an IR absorption (recorded as a percent transmittance) is proportional to the dipole moment of the vibration (Figure 4). For the purposes of organic chemistry, this “back of the envelope” conceptualization is communicated to students as a variation on the foundational analysis of dipole moment as approximated by considering the electro negativities of the atoms involved in specific functional groups. Coupled to this is an estimation of molecular structure with a nod toward molecular symmetry. In other words, asymmetric, highly polar bonds like carbonyl groups have intense IR absorptions; systems in which the dipoles cancel register little or no IR signal. To a first-level approximation, the reverse is true for Raman spectroscopy because the intensity of those signals is proportional to the square of the product of the molecular polarizability and the local electric field (the product of which is known as the molecular induced dipole, µfi) (19, 20).

Figure 3. IR (left y-axis, signal at top) and Raman (right y-axis, signal at bottom) spectra for 2,5-di-tert-butyl-1,4-dimethoxybenzene. Important features of the spectra are defined in the text. The symbols (s) and (a) indicate symmetric and asymmetric stretches, respectively. The asterisk (*) indicates ambient light contamination. 39 Sonntag; Raman Spectroscopy in the Undergraduate Curriculum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

Figure 4. Raman intensity (left), I, is proportional to the square of the product of the molecular polarizability(α) and the local electric field (E). IR intensity (right), I, is proportional to the dipole moment of the vibration (µ). Sample molecules that illustrate these concepts include cyclohexanone, hex1-yne, and hex-3-yne (Figure 5). The IR spectrum of cyclohexanone exhibits a classic carbony absorption band at 1,716 cm-1 (4% transmittance) (21). This very intense signal is due to the large dipole which is in turn related to the large difference in electronegativity of carbon and oxygen. Similarly, the carbon-carbon triple-bond stretch in hex-1-yne exhibits a diagnostic IR signal at 2,120 cm-1 (49% transmittance) (22). In this case the asymmetric substitution of the alkene (alkyl on one end, hydrogen on the other) results in a medium signal that is readily apparent in the triple-bond stretching region of the IR spectrum. However, hex-3-yne is transparent to IR radiation in this region because the symmetric stretching of the triple bond results in no change in its dipole. However, the signal in the Raman spectrum is predicted to be strong. Computational predictions for this stretch in the gas phase put the carbon-carbon triple-bond stretch at 2,365 cm-1 with the very low IR intensity of 0.0014 versus the very high Raman intensity of 286 (a ratio 1 to >200,000) (23, 24). More detailed data that support these assertions can be found in literature readily accessible to undergraduate students. In addition, students can execute quantum chemical calculations to support and contextualize their findings. Several chapters in this Volume speak to laboratory experiments that put these tools into students’ hands (24).

Figure 5. Cyclohexanone (left), hex-1-yne (middle), and hex-3-yne (right), three molecules that illustrate the intensity of Raman and IR signals. Returning to Figure 3, several comparisons between the two spectra are readily apparent. In the oft-ignored carbon-hydrogen bond stretching region, the generic C–H stretches are joined by a Raman-active symmetric (s) aryl (Ar) C–H stretch. While students may only be able to assign this signal by looking at the results of a calculation, faculty can introduce leading question (“What C–H stretches could result in cancellation of dipoles?”) to direct students toward structurally-based answers. The Raman signal at 1,612 cm-1 is the symmetric carbon-carbon double-bond (C=C) stretch in the benzene ring, a feature students may be able to predict with and IR correlation table. Other Raman signals of note (that would probably require calculations to assign) include the asymmetric (a) Ar C–H wag (1,282 cm-1) and the (a) breathing mode (706 cm-1), both of which have small or negligible IR signals. Conversely, the IR-active (a) Ar C–H wag at 1,206 cm-1 has a corresponding Raman signal of lower relative intensity. 40 Sonntag; Raman Spectroscopy in the Undergraduate Curriculum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

Overall, the spectra for 2,5-di-tert-butyl-1,4-dimethoxybenzene appear to be accessible to students enrolled in the two-semester organic chemistry sequence. One envisions a laboratory period in which students take one more spectrum, a process that takes little extra time, supported by lecture or discussion group time dedicated toward interpreting the spectra at an elementary level. Support from computations could be optional (although desirable) but in all cases students’ attention would be focused on foundational concepts of molecular structure and symmetry. Calculations, and perhaps even the synthesis of an authentic sample of the 1,2-di-tert-butyl isomer (not a trivial task (25)), have the potential to resolve the question of unambiguous assignment of regioisomer by the comparison of Raman and IR signals. Laboratory exercises designed to explore this possibility are ongoing and will be reported in due course.

Distinguishing Stereoisomers in a Diels-Alder Reaction The Diels-Alder reaction, a paradigm of electrocyclic addition reactions, is governed by the endo rule which indicates that the endo stereoisomer typically predominates over the exo stereoisomer (Figure 6). When students prepare bicyclo[2.2.1]hept-5-ene-endo-2,3-dicarboxylic anhydride from cyclopentadiene and maleic anhydride, they use the endo rule rationalized by secondary orbital overlap to explain which stereoisomer they observed (15). However, in the absence of an authentic sample of the exo product for comparison, these rationalizations leave something to be desired. Can Raman spectroscopy help to allow for a more unambiguous structural assignment? What other features of the molecule can data from a Raman spectrum elucidate for these students? Spectra obtained from student samples of bicyclo[2.2.1]hept-5-ene-endo2,3-dicarboxylic anhydride are presented in Figure 7 (18). The carbon--hydrogen stretching region illustrates the foundational principles of dipole moment and polarizability (Figure 4) as the C – H stretches have weak IR intensities due to small changes in dipole moment (Δµ) but strong Raman intensities due to large changes in polarizability (Δα). The carbonyl stretching region of the spectra illustrates the difference between α and µ much more clearly. In the Raman spectrum the intensities for both the symmetric (s) and asymmetric (a) carbonyl (C=O) stretches (1,839 and 1,768 cm-1, respectively) are nearly equivalent. Students may therefore conclude that both stretches have similar changes in α despite the change from ground-state to excited-state vibrational level. However, the (s) C=O stretch (1,843 cm-1) experiences a cancellation in µ that results in a smaller IR signal for that band than the corresponding (a) C=O stretch (1,767 cm-1) that experiences a large Δµ. Finally, the (s) carbon-carbon double bond (C=C) stretch at 1,569 cm-1 is quite intense in the Raman spectrum and nearly indistinguishable from background in the IR spectrum. This analysis alone demonstrates the added value of comparing Raman to IR spectra as the explanation gets lost or confused without the data to illustrate that the C=C is vibrating regardless of whether a peak appears in the IR spectrum.

41 Sonntag; Raman Spectroscopy in the Undergraduate Curriculum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

Figure 6. The reaction of cyclopentadiene and maleic anhydride to prepare bicyclo[2.2.1]hept-5-ene-endo-2,3-dicarboxylic anhydride (left product) and its exo stereoisomer (right product).

Figure 7. IR (left y-axis, signal at top) and Raman (right y-axis, signal at bottom) spectra for bicyclo[2.2.1]hept-5-ene-endo-2,3-dicarboxylic anhydride. Important features of the spectra are defined in the text. The symbols (s) and (a) indicate symmetric and asymmetric stretches, respectively. Symbols α and µ are defined in Figure 4. The asterisk (*) indicates ambient light contamination. Identifying the endo and exo stereoisomers using Raman spectroscopy would be facilitated by both the synthesis of the authentic exo isomer and by comparison of calculated and experimental spectra. Future plans for the laboratory sequence at Albright College include synthesis of the exo isomer by high-temperature isomerization of the endo product. This chemistry is accessible to undergraduate students (26). Preliminary calculations suggest measurable (6-16 cm-1) differences in the symmetric and asymmetric stretches of the lone methylene (–CH2–) group and the C–H groups alpha to the carbonyl groups (24, 27). While it is not clear that such differences will enhance the pedagogically 42 Sonntag; Raman Spectroscopy in the Undergraduate Curriculum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

important illustration provided by the C=C stretch, they provide a starting point in the search for relevant examples.

Investigating Isotope Effects in an Aldol Reaction The aldol reaction allows students to generate carbon-carbon singleand double bonds from aldehydes and ketones (at least one with an alpha hydrogen). This robust reaction highlights historically important chemistry (for example, the Robinson annulation (28)) with both modern applications and implications for the study of biochemistry (specifically, glycolysis (29)). In the curriculum at Albright College, students prepare trans-p-anisalacetophenone [(E)-3-(4-methoxyphenyl)-1-phenylprop-2-en-1-one] from acetophenone and p-anisaldehyde (Figure 8) (16).

Figure 8. The base-catalyzed reaction of acetophenone (left starting material) and p-anisaldehyde (right starting material) to yield p-anisalacetophenone (right), performed in ethanol as solvent.

Figure 9 contains the Raman and IR spectra for p-anisalacetophenone and as in previous figures there are features highlighted that may be used as examples of the complementarity of these techniques (18). The relatively strong C=O stretch in the IR spectrum (large Δµ) has a relatively weak (but nonzero) counterpart in the Raman spectrum (small Δα). Both of these signals are found at 1,657 cm-1. Conversely, the dominant Raman C=C stretch at 1587 cm-1 is flanked by the overlapping 1,596 and 1,578 cm-1 IR signals (which are almost equally intense as the C=O stretch). Here, changes in intensity and position correspond to changes in identity (aryl versus methoxyaryl versus vinyl). While these cannot be individually assigned (except, perhaps, with computational support), these data illustrate that p-anisalacetophenone may play a role in curriculum development aimed at introducing Raman spectroscopy in the organic chemistry curriculum. While it is desirable to compare cis and trans stereoisomers using Raman spectroscopy, the problems previously encountered plague this synthesis as well, namely the challenge of synthesizing authentic cis product and the lack of diagnostic absorption modes (which would be addressed using calculations). However, the ease of synthesis for p-anisalacetophenone and the availability of deuterated starting materials at a reasonable cost offers the opportunity for the specific deuteration of this molecule at the ring, α, and ß positions (Figure 10) (30). 43 Sonntag; Raman Spectroscopy in the Undergraduate Curriculum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

Figure 9. IR (left y-axis, signal at top) and Raman (right y-axis, signal at bottom) spectra for p-anisalacetophenone. Important features of the spectra are defined in the text. The asterisk (*) indicates ambient light contamination.

Figure 10. Specific deuteration may be readily achieved at the ring, α, and ß positions by selecting the appropriate deuterated precursor(s).


Since Raman signals, like IR signals, are subject to changes in frequency due to changes in atomic mass, these derivatives allow organic chemistry students to be introduced to the effects of isotopic substitution and to observe the corresponding change in these spectra. Goals for the student in this type of experiment build on prior knowledge and set the stage for later knowledge acquisition. Correlating experimental IR signals to specific C–H versus C–D substitutions using calculated values confirms and extends students’ previous knowledge about IR spectra. Assigning Raman signals and determining the effect of C–H versus C–D substitutions on these signals provides reinforcement of students’ nascent knowledge about Raman spectra. Note that changes in frequency (Δν) may be evaluated mathematically using the frequency of motion equation (Figure 11) (20). This approach directly connects concepts developed in organic chemistry to concepts that will be developed more fully in physical chemistry. Spectra of all-hydrogen, ring-deuterated, and ß-deuterated p-anisalacetophenone are provided in Figure 12 (aromatic region, 3200-2600 cm-1; next page) and Figure 13 (C=O/C=C and fingerprint regions, 1800-600 cm-1; next following page) (18). Preliminary analysis confirms that some vibrations are affected by deuteration, as expected: dashed vertical lines provide examples of signals that change in either one or both deuterated spectra; signals that may serve as controls are indicated by solid vertical lines. While further development is ongoing, these spectra provide evidence that p-anisaldehyde is worthy of development into an organic chemistry activity that helps to bridge the gap as students advance toward the study of physical chemistry.

Figure 11. The frequency of motion equation, where νo is the frequency of motion, κ is the force constant, and µ is the reduced mass.


Figure 12. Aromatic region of IR (left y-axis, signal at top) and Raman (right y-axis, signal at bottom) spectra for p-anisalacetophenone (all H, top; ring-deuterated, middle; ß-deuterated, bottom). Solid vertical lines suggest signals apparently not affected by deuteration; dashed vertical lines suggest signals affected by deuteration. Important features of the spectra are defined in the text. (These indications are illustrative and are not exhaustive.)


Figure 13. Double bond and fingerprint region of IR (left y-axis, signal at top) and Raman (right y-axis, signal at bottom) spectra for p-anisalacetophenone (all H, top; ring-deuterated, middle; ß-deuterated, bottom). Solid vertical lines suggest signals apparently not affected by deuteration; dashed vertical lines suggest signals affected by deuteration. Important features of the spectra are defined in the text. (These indications are illustrative and are not exhaustive.)


Summary and Future Directions In this chapter, three paradigms for the incorporation of Raman spectroscopy into the organic chemistry curriculum were explored. Reaction products from electrophilic aromatic substitution, the Diels-Alder reaction, and the aldol reaction are already subjected to IR spectroscopy. Thus, they are appropriate starting points for complementary study using Raman spectroscopy. In each case, IR theory is reinforced (for example, excitation requires a change in the bond dipole by comparison to the parallel rule for Raman spectroscopy (excitation requires a change in polarization). This is accomplished with some extra time and effort but not an onerous amount; the benefits – better preparation for physical chemistry – may outweigh the use of additional resources. With an honors module or majors only section it might be possible to study symmetry in a more detailed way or to introduce the selection rules at the organic chemistry level. Conversely, the study of these molecules in organic chemistry could become examples for the study of these concepts in physical chemistry or other advanced courses (31). Excitingly, other potential uses of Raman spectroscopy include the assignment of regiochemistry and stereochemistry to reaction products as well as the analysis of deuterated materials. In addition, each of these approaches may be applied to other reactions and products (32). Support from applied computational chemistry, which has already arrived as an important tool for the study of spectroscopy (4), will be invaluable in the development of the projects suggested in and by this chapter (33). The call to integrate Raman spectroscopy into the organic chemistry curriculum both to complement the study of IR spectroscopy and to better prepare students moving on to the study of physical chemistry is answered by considering spectra of small molecules in the context of a prerequisite course. Thus, the foundations for the deeper study of the theory and applications of Raman spectroscopy are set. This can be done without disrupting or over-packing the current organic chemistry curriculum because the synthesis and instrumental analysis pieces are already well established. Successful implementation will be evaluated with assessment. In summary, the focus of this chapter is the story of how interactions between colleagues result in the implementation of advanced instrumental techniques in authentic curricular ways, offering the possibility of enhanced student learning outcomes. The context of this story is Albright College, a small, liberal arts college in Pennsylvania, whose ACS-accredited curriculum supports an emphasis on optical molecular spectroscopy. The raison d'être for this story is the observation made by Sir Chandrasekhara Venkata Raman who was studying the interaction of light with matter when he discovered that “the packet of energy colliding with the molecule mostly gives up part of its energy to the molecule which is excited, and the remainder is exhibited as a modified colour (1).” Raman scattering – also called the Raman effect – has become the foundation of an important analytical technique that detects vibrational and rotational modes of molecules and materials. It most directly complements the vibrational behavior of molecules and materials observed using infrared spectroscopy. This momentous discovery was honored in 1998 by the American Chemical Society, jointly with the Indian Association for the Cultivation of Science, with the creation of an 48 Sonntag; Raman Spectroscopy in the Undergraduate Curriculum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

International Historic Chemical Landmark (34). The Landmark is located in the Indian Association for the Cultivation of Science in Kolkata, India (35). With the advent of affordable benchtop instruments and engaging laboratory experiments, this powerful technique is now fully available to undergraduate students.

Acknowledgments In addition to those whose contributions were already acknowledged in the references, the authors thank the following for their contributions: Victoria Orzechowski (Librarian, Othmer Library of Chemical History at the Chemical Heritage Foundation) provided guidance on finding and citing the original articles on Raman spectroscopy; the Professional Council, the Undergraduate Research Committee, and the Albright Creative Research Experience Program at Albright College provided funding; and the National Science Foundation (CSH: TG-CHE150026) provided supercomputer access through the Extreme Science and Engineering Discovery Environment (XSEDE).

References Chem. Age (London), Indian Chemical Notes, 1931, 24, 168. Raman Effect. J. Chem. Educ., 1931, 8, 1287. The Nobel Prize in Physics 1930. http://www.nobelprize.org/nobel_prizes/ physics/laureates/1930/ (accessed May 30, 2018). 4. Villars, D. S. The Raman Spectrum of Dioxane. J. Am. Chem. Soc. 1930, 52, 4612–4613. 5. Reynolds, N. B.; Benford, F. An Apparatus for the Demonstration of the Raman Effect in Liquids. Rev. Sci. Instrum. 1930, 1, 413–416. 6. Hamann, C. S. Sonntag, M. D. Introduction to Raman Spectroscopy in the Undergraduate Curriculum. In Raman Spectroscopy in the Undergraduate Curriculum; Sonntag, M. D., Ed.; ACS Symposium Series 1305; American Chemical Society: Washington, DC, 2018; Chapter 1. 7. Artz, P. G. Department Chair, personal communication. 8. Committee on Professional Training. https://www.acs.org/content/acs/en/about/ governance/committees/training.html (accessed May 30, 2018). 9. Committee on Professional Training. Undergraduate Professional Training in Chemistry. ACS Guidelines and Evaluation Procedures for Bachelor’s Degree Programs. https://www.acs.org/content/dam/acsorg/about/governance/ committees/training/2015-acs-guidelines-for-bachelors-degree-programs.pdf (accessed May 30, 2018). 10. Young, S. C.; Smith, K. T.; DeBlasio, J. W.; Hamann, C. S. Utilizing NMR to Study Structure and Equilibrium in the Organic Chemistry Laboratory. In NMR Spectroscopy in the Undergraduate Curriculum: First Year and Organic Chemistry Courses, Volume 2; Soulsby, D., Anna, L. J., Wallner, A. S., Eds.; ACS Symposium Series 1221; American Chemical Society: Washington, DC, 2016; pp 119−136. 1. 2. 3.


11. For an example of scaffolding of experiments see: Shuldburg, S.; Carroll, J. Scaffolding Students’ Skill Development by First Introducing Advanced Techniques through the Synthesis and 15N NMR Analysis of Cinnamamides. J. Chem. Educ. 2017, 94, 1974–1977. 12. Smith, K. T.; Hamann, C. S. Using Esters to Construct Chemical Shift Correlation and Introduce First-Order Coupling. J. Chem. Educ. 2017, 94, 126–130. 13. Polito, V.; Hamann, C. S.; Rhile, I. J. Carbocation Rearrangement in an Electrophilic Aromatic Substitution Discovery Laboratory. J. Chem. Educ. 2010, 87, 969–970. 14. Maskornick, M. V.; Polito, V.; Rhile, I. J.; Hamann, C. S. Carbocation Rearrangements in the Undergraduate Laboratory: GC/MS and NMR Deduction of Products from Electrophilic Aromatic Substitution in a Discovery Laboratory Experiment. Book of Abstracts, 250th National Meeting of the American Chemical Society, Boston, MA, Aug 16-20, 2015; American Chemical Society: Washington, DC, 2017; CHED 476. 15. Gilbert, J. C.; Martin, S. F. Experimental Organic Chemistry: A Miniscale and Microscale Approach, 6th ed.; Brooks/Cole Cengage Learning: Boston, MA, 2016; pp 421−442. 16. Gilbert, J. C.; Martin, S. F. Experimental Organic Chemistry: A Miniscale and Microscale Approach, 6th ed.; Brooks/Cole Cengage Learning: Boston, MA, 2016; pp 673−714. 17. Zehr, J. D.; Hamann, C. S. Combining X-Ray Crystallography and Computational Chemistry with Nuclear Magnetic Resonance Spectroscopy for Small Molecule Structural Characterization; Book of Abstracts, 252nd National Meeting of the American Chemical Society, Philadelphia, PA, Aug 21-25, 2016; American Chemical Society: Washington, DC, 2016; CHED 349. 18. Hantz, E. R.; Sonntag, M. D.; Hamann, C. S. unpublished results. Raman spectra were obtained on a B&W Tek I-Raman Plus 532nm excitation system with a 20x objective. Laser power was varied between 20 – 50 mW and 10-20 second integrations. Spectra were background subtracted to remove ambient light. Infrared spectra were obtained on a Perkin-Elmer Frontier FT-IR fitted with an ATR accessory. Spectra consisted of 16 scans and were background subtracted. 19. Crouch, S. R.; Skoog, D. A.; Holler, J. F. Principles of Instrumental Analysis, 7th ed.; Cengage Learning: Boston, MA, 2018; pp 389−452. 20. Laidler, K. J.; Meiser, J. H.; Sanctuary, B. C. Physical Chemistry, 4th ed. Houghton Mifflin Company: Boston, MA, 2003; pp 636−713. 21. Spectral Database for Organic Compounds, SDBS, AIST. http://sdbs.db.aist.go.jp/sdbs/cgi-bin/direct_frame_disp.cgi?sdbsno=571 (accessed May 30, 2018). 22. Spectral Database for Organic Compounds, SDBS, AIST. http://sdbs.db.aist.go.jp/sdbs/cgi-bin/direct_frame_disp.cgi?sdbsno=568 (accessed May 30, 2018). 23. Palazzo, T. A. Aarhus University, personal communication. 24. Calculations discussed in this paper were performed with Gaussion09, Revision C.01 or D using the B3LYP method and the 6-31+g(d,p) basis set. Calculated frequencies vary slightly from experimental frequencies because calculated frequencies are evaluated in the gas phase. Students can confirm the identity


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of a particular frequency by viewing the animated motion using GaussView 5.0. M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, T. Keith, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, and D. J. Fox Gaussian, Inc., Wallingford, CT, 2010. Bergman, R. G. University of California, Berkeley, personal communication. Rablen, P. R. Swarthmore College, personal communication. Hamann, C. S., unpublished results. Delaude, L.; Grandjean, J.; Noels, A. F. The Step-by-Step Robinson Annulation of Chalcone and Ethyl Acetoacetate. An Advanced Undergraduate Project in Organic Synthesis and Structural Analysis. J. Chem. Educ. 2006, 83, 1225. Bodner, G. M. Metabolism Part I: Glycolysis for the Embden-Meyerhoff Pathway. J. Chem. Educ. 1986, 63, 566. Gehman, C. A.; Hamann, C. S. Distinguishing Aromatic and Alkene NMR Signals Using Specifically Deuterated Chalcones. Book of Abstracts, 253rd National Meeting of the American Chemical Society, San Francisco, CA, Apr 2-6, 2017; American Chemical Society: Washington, DC, 2017; CHED 99. See, for example: Srinivasan, S.; Reisner, B. A.; Smith, S. R.; Stewart, J. L.; Johnson, A. R.; Vin, S.; Marek, K. A.; Nataro, C.; Murphy, K. L.; Raker, J. R. Historical Analysis of the Inorganic Chemistry CurriculumUsing ACS Examinations as Artifacts. J. Chem. Educ. 2018, 95, 726–733. See, for example: Jarret, R. M.; New, J.; Hurley, R.; Gillooly, L. Looking beyond the endo Rule in a Diels-Alder Discovery Lab. J. Chem. Educ. 2001, 78, 1262–1263. See, for example: Peterson, K. I.; Pullman, D. P. Determining the Structure of Oxalate Anion Using Infrared and Raman Spectroscopy Coupled with Gaussian Calculations. J. Chem. Educ. 2016, 93, 1130–1133. C.V. Raman and the Raman Effect. International Historic Chemical Landmark.. http://www.acs.org/content/acs/en/education/whatischemistry/landmarks/ ramaneffect.html (accessed May 30, 2018). Bohning. J. J.; Misra, T. N.; Choudhury, M. The Raman Effect. https:/ /www.acs.org/content/dam/acsorg/education/whatischemistry/landmarks/ ramaneffect/the-raman-effect-commemorative-booklet.pdf (accessed May 30, 2018).


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