67
Anal. Chem. 1904, 56,67-70 (12) (13) (14) (15) (16)
Jones, P. F. folym. Left. 1966, 6, 487. Bergman, I. Nature (London) 1966, 278, 396. Stevens, B. U S . Patent 3612866, Oct 12, 1971. Knopp, J. A.; Longmulr, I. A. Biochim. Blophys. Acta 1972, 279, 393. Lubbers, D. W.; Optlz, N. Z.Naturforsch., C: Blosci. 1975, 30C, 532.
(17) Stern, 0.; Volmer, M. fhyslk. Z.1919, 20, 183. (18) Peterson, J. I.; Sullivan, J. V. Rev. Scl. Instrum, in press.
for review
5 , 1983* Accepted September 16,
1983.
Rules for Computerized Interpretation of Vapor-Phase Infrared Spectra Sterling A. Tomellini,* James M. Stevenson, and Hugh B. Woodruff
Merck Sharp & Dohme Research Laboratories, P.O. Box 2000, Rahway, New Jersey 07065
Rules for the Interpretationof vapor-phase Infrared spectra have been developed for the IBM 3081 version of the Woodruff and Smith program for the analysls of Infrared spectra (PAIRS) and Its Nlcolet 1180 version known as the Merck Infrared spectral lnterpretatlon package (MrsIP). Necessary changes and additions were made to the rules, rule complier, and Interpreter. Over 75 4-cm-’ resolution vapor-phase spectra were tested along with a number of condensed-phase spectra to ensure the proper functioning of the new rules and the uncompromlsed nature of the prevlously developed condensed-phase rules. The addltlonal capablllty of the lnterpreter along with Its avallablllty on an Instrument-based mlnlcomputer will give those sclentlsts employlng techniques such as GWFTIR, off-gas, and head space analysls on larger organic molecules at moderate resolution an alternative to currently available matching techniques.
The Woodruff and Smith program for the interpretation of infrared spectra (PAIRS) (1, 2) was designed to aid the chemist in interpreting infrared spectra of condensed-phase (liquid or solid) compounds. Recent adaptation of this program to an instrument-based minicomputer (3) provided the opportunity to expand the interpretation capabilities of PAIRS. Compounds have different infrared spectra in various condensed phases and the vapor phase due to changes in hydrogen bonding, the dielectric constant of the medium, and nonpolar solvent-solute interactions. Hence, attempts to interpret vapor-phase spectra with condensed-phaseinterpretation rules proved to be unacceptable. Welti ( 4 ) has given frequency correlation charts for some of those compounds known to have different vapor and condensed-phase spectra. Examples include alcohols, phenols, amines, amides, esters, and ketones. This book is the primary reference for the modification of previous interpretation rules and generation of new rules. Additional refinement was made by use of other recently published correlation charts of the -OH stretching region (5) and a number of 4-cm-’ resolution vapor-phase spectra. These spectra were provided by the Nicolet Instrument Corp. (Madison, WI) and were produced by Sadtler Research Laboratories Inc. (Philadelphia, PA) for Leo V. Azarraga of EPA. This paper reports the development of vapor-phase interpretation rules for both the IBM mainframe version of PAIRS and the Nicolet 1180/1280 version known as MISIP (Merck infrared spectral interpretation package). Explanation of the 0003-2700/84/0356-0067$01.50/0
programming changes necessary to utilize these new rules and examples are presented. EQUIPMENT
A Nicolet 1180 minicomputer with 40K of 20 bit word semiconductor memory and mass storage consisting of a Diablo Model 44B dual disk system having a capacity of 4.5 megawords was used for all development work. This computer is a component of our Nicolet 7199 FTIR system. Full use was made of existing Nicolet system software. Corresponding modifications of PAIRS software were made with an IBM 3081 computer. Transfer of interpretation rules from the Nicolet 1180 to the IBM system was made at 1200 baud with a phone modem connection through a Digital VT 125 terminal via a VAX 11/780. PROGRAM DESCRIPTION
As described previously (1-3) the interpretation package consists of an interpreter program, a set of interpretation rules in an English-like language called CONCISE (computer oriented notation concerning infrared spectral evaluation), a rule compiler program, and a set of compiled rules used as data by the interpretation program. All components exist on both the Nicolet and IBM systems. The interpreter is written in FORTRAN and treats the compiled rules and spectral information (peak width, position, intensity, sample state) as data. Due to the design of the interpreter, only minor FORTRAN changes were necessary to expand its capabilities to include vapor-phase spectra. Those changes consisted mainly of input and output modifications leaving the computational algorithm of the program unchanged. The rule compiler is also written in FORTRAN and translates interpretation rules in CONCISE into more compact integer strings. Major changes were required for both the IBM and Nicolet versions of the rule compiler. Due to differences in the two versions, required by different word sizes and computational speeds of the IBM 3081 and Nicolet 1180, the changes were not identical but are entirely user transparent. Modifications were made to existing subroutines, dictionary, and internal tables to accommodate “vapor”as a sample state. The CONCISE language was expanded to include “vapor” as a sample state, thus’ allowing the creation of specific vapor-phase rules and the modification of existing condensedphase rules. Major changes, additions and deletions, were necessary to the existing interpretation rules in CONCISE. The approach generally followed was to add specific vapor-phase conditions 0 1983 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 56, NO. 1, JANUARY 1984
88
N
9 -1
4-METHYL-2-PENTRYOl LIQUID
c
p’: c
%W
! ‘D
*
9 Y
WRVENUHBERS
Flgure 1.
Liquid-phase spectrum of 4-methyl-2-pentanol.
Table I. The 16 Largest Peaks as Determined by the Peak Picking Routine for Liquid-PhaseSpectrum of 4-Methyl-2-pentanol peak no.
position CM- 1
re1 intens
width
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
8 28 9 26 1017 1057 1116 11 54 1275 1312 1344 1369 1412 1469 2872 2918 2960 3345
2 3 3 3 3 3 2 2 2 4 2 3 5 6 10 5
2 2 2 2 2 2 2 2 2 2 3 2 2 2 2 3
Table 11. The 11 Largest Peaks as Determined by the Peak Picking Routine for Vapor-Phase Spectrum of 4-Methyl-2-pentanol
Flgure 2.
peak no.
position CM-1
re1 intens
width
1 2 3 4 5 6 7 8 9 10 11
924 1025 1053 1089 1148 1244 1380 1468 2927 2969 3655
1 1 1 2 2 1 2 1 5 10 1
2 2 2 2 2 2 2 2 3 2 2
Vapor-phase spectrum of 4-methyl-2-pentanol.
to existing condensed-phase rules which have already undergone substantial testing and have proven to be quite useful for liquid and solid-state spectra. Thus if one requests an interpretation of a nonvapor speqtrum, interpretation will be made by using essentially the same rules as were previously described (1-3). When a sample state of “vapor” is declared, those functionalities which show distinct spectral changes between the vapor and condensed phases and for which adequate correlation charts are available (e.g., alcohol) will be interpreted by use of the new vapor-phase rules. Those functionalities for which limited vapor correlation charb exist but which are expected to show vastly different infrared spectra on change of physical state (e.g., lactam) are disregarded when sample state is assigned as “vapor”. The design of the computerized interpretation package which treats rules as data will accommodate easy rule modification with the procurement of sufficient spectral data for those functionalities to allow the development of satisfactory correlation charts.
RESULTS AND DISCUSSION An example of the difference between vapor-phase and liquid-phase spectra of compounds which are predominately hydrogen bonded in the condensed phase can be seen in Figures 1 and 2. Both spectra are of 4-methyl-2-pentanol; one is taken as a liquid between KBr plates (Figure 1) and the other is a vapor-phase spectrum (Figure 2). Both spectra are 4 cm-l resolution. The -OH stretching frequency of the liquid is 3345 cm-l and is broad while the vapor spectrum shows an -OH stretching frequency of 3655 cm-l with average width. Other peak intensities, widths and positions are given in Table I for the liquid-phase spectrum and Table I1 for the
Table 111. The Interpretation Results for Liquid-Phase 4-Methyl-2-pentanolwith Condensed Phase Rules, Sample State of “Neat” 1 2 3 4 5 6
group name
probability
alcohol methyl methylene amine-tertiary amine amine-secondary
0.75 0.65 0.49 0.40 0.40 0.3 5
Table IV. The Interpretation Results for Vapor-Phase 4-Methyl-2-pentanol with Condensed-PhaseRules, Sample State of “Other” group name probability 1 2 3 4
amine amine-tertiary acid methyl
0.40 0.40
0.35 0.30
-
vapor-phase spectrum. The intensities are normalized from 1 to 10 with 10 being the strongest peak and the widths are given values of 1,2, or 3 corresponding to sharp (fwhh 12 cm-l), average, or broad (fwhh > 75 cm-l), respectively. The data in Table I were interpreted by use of condensed-phase interpretation rules and the results are presented in Table 111. It can be seen that the interpreter correctly predicts the presence of the alcohol and methyl functionalities with high expectation values for the liquid spectrum. If the data from the vapor-phase spectrum, Table 11, are interpreted by using
ANALYTICAL CHEMISTRY, VOL. 56, NO. 1, JANUARY 1984
Table V. The Interpretation Results for Vapor-Phase 4-Methyl-2-pentanol with Modified Rules, Sample State of “Vapor” group name probability alcohol alcohol-secondary amine amine-1-a:- branch alcohol-primary amine-2-ali methyl
1
2 3 4 5 6 7
0.85 0.55 0.40 0.40 0.3 5 0.35 0.30
-
Table VII. The Interpretation Results for Vapor-Phase 6-Amino-2-methyl-2-heptanol with Condensed Phase Rules, Sample State of “Other” group name probability 1
2 3
781 912 933 1027 1160 1215 1338 1378 1466 1621 2941 2972 3643
2 3
4 5 6 7 8
9 10 11
12 13
3 2 2 1 3
2 1
4 2 1
7 10 1
2 2 2 3 3 3 3 2 2 2 2 2 2
1
2 3 4 5 6 7 8 9
0.45 0.40 0.40
group name
probability
alcohol amine -branch amine-1-CY alcohol-tertiary amine-1-n-ali alcohol-secondary methyl amine-2-ali alcohol-primary
0.90 0.90 0.90 0.60 0.50 0.50 0.45 0.40 0.40
~~
Table IX. The 13 Largest Peaks as Determined by the Peak Picking Routine for the Vapor-Phase Spectrum of Heptanoic Acid position re1 CM-1 intens width 1
2 3
4 5 6 7
6-AMINO-2-BETHY L-2-HEPTANOL
?{
methyl amine-tertiary amine
Table VIII. The Interpretation Results for Vapor-Phase 6-Amino-2-methyl-2-heptanol with Modified Rules, Sample State of “Vapor”
Table VI. The 13 Largest Peaks as Determined by the Peak Picking Routine for the Vapor-Phase Spectrum of 6-Amino-2-methyl-2-heptanol peak position re1 no. CM-1 intens width 1
69
8
9 10
I\
11
12 13
511 558 607 1098 1138 1282 1383 1462 1779 2877 2939 296 7 3577
2 2 3 2 2 3 2 2 2 2 2 2 2
1 2 2 5 5 1 2 1 10
3 6 5 4
HEPlANOlC A l l @
do” Flgure 3.
Vapor-phase spectrum of 6-amino-2-methyl-2-heptanol.
condensed-phase rules, the resultant interpretation is unsatisfactory and is presented in Table IV. The expectation values of 0.40 for “amine” and 0.35 for “acid” indicate that although these two functionalities are the most likely to be present in the molecule, the evidence is not overly strong. If the data in Table I1 are interpreted as being vapor-phase data using the modified rules containing vapor correlations, the resulting interpretation is presented in Table V. “Alcohol” is correctly predicted with a good degree of certainty and the further distinction of “secondary alcohol” is likewise correct. There is some likelihood of an amine being present, but the likelihood of an alcohol is much greater. The vapor spectrum of 6-amino-2-methyl-2-heptanol is shown in Figure 3 with peak data presented in Table VI. Notice the lack of intensity in the NH symmetric stretching region (approximately 3300 cm-l) (4). IR spectra of amines in the vapor state often show little evidence of NH stretching vibrations. If the data in Table VI are input into the interpreter ind treated as condensed-phase data, the interpretation results shown in Table VI1 are returned. It is apparent that
‘I
6
URVENUHRERS
Flgure 4.
Vapor-phase spectrum of heptanoic acid.
interpretation as condensed-phase data yields low expectation values for “amines” and no expectation that an alcohol is present a t all. Interpretation of the data in Table VI using the modified rules with the stipulation that the spectrum was taken as a vapor yields the results presented in Table VIII. Alcohol and amine functionalities are both returned with large expectation values. In addition further distinctions are made as to the type of alcohol, tertiary, and the type of amine, primary branched (1-a-branch). In this case both subclasses
70
ANALYTICAL CHEMISTRY, VOL. 56, NO. 1, JANUARY 1984
Table X. The Interpretation Results for Vapor-Phase Heptanoic Acid with Modified Rules, Sample State of ‘‘Vapor” 1 2
3 4 5 6 7 8 9 10 11
group name
probability
acid acid-saturated acid-cr-branched ester-(of-CO2H) lactone+ -sat ketone ketone-5-ring methyl amine amine-2-ali ketone-sat
0.90 0.90 0.62 0.50 0.50 0.47 0.47 0.4 5 0.30 0.30 0.30
Table XI. The 14 Largest Peaks as Determined by the Peak Picking Routine for the Vapor-Phase Spectrum of 4-Phenyl-2-butanone peak no. 1 2
3 4 5 6 7 8 9 10 11 12 13 14
position CM-1 499 697 743 1158 1208 1363 1448 1497 1604 1734 2933 2963 3036 3072
re1 intens 1
4 3 4 1 4 2 2 1
10 2
2 3 3
width 2 2 2 2 2 2 2 2 2 2 2 2 2 2
4-PHENYL-2-RUTANONE
fa+
Table XII. The Interpretation Results for Vapor-Phase 4-Phenyl-2-butanone with Modified Rules, Sample State of “Vapor” 1
2 3 4
AA Flgure 5. Vapor-phase spectrum of 4-phenyl-2-butanone.
are correct; however, the program tends to place more certainty in indicating class (e.g., alcohol) than subclass (e.g., tertiary) correctly. Acids are another functionality which have markedly different spectra when taken in the vapor and condensed states. Figure 4 shows the vapor spectrum of heptanoic acid. Table IX contains the peak data as entered into the interpretation program. Two characteristic differences between a vaporphase and condensed-phaseacid spectrum are higher carbonyl stretching frequency (1779 cm-l) and sharper hydroxyl stretch absorptions (width = 2). The interpretation results obtained by using a sample state of vapor are presented in Table X. The interpreter correctly suggests “acid”, particularly “saturated acid”, as being present. Also reported with some expectation are ”acid-a-branched”and “ester” as well as other carbonyl containing functionalities, but all with lower expectation values. Had the data in Table IX been entered with a sample state other than vapor, the ketone functionality, especially a four-membered ring ketone, would have been predicted to be most likely present. As a final example, the vapor spectrum of 4-phenyl-2-butanone is shown in Figure 5 with peak data presented in Table XI and interpretation results shown in Table XII. The interpreter correctly predicts the ketone and aromatic functionalities to be present with high expectation values when the sample state is entered as vapor. The only other carbonyl functionality returned is “amide” with a much lower expectation value. Had the data been entered as being a condensed-phase spectrum, ”aromatic” would still have been predicted with the same expectation value, but “ketone”would
5
6 7 8
group name
probability
ketone ketone-sat aromatic olefin-CHR=CHR(C) olefin-(nonarom) amide amide-primary methyl
0.75 0.75 0.65 0.60 0.60 0.50 0.50 0.35
have been placed below “lactam” in certainty of presence. These examples demonstrate the need for vapor-phase interpretation rules and are indicative of the success which we have had in developing such rules for functionalities where frequency correlations exist. The underlying philosophy of MISIPand PAIRShas been maintained with the new set of rules, namely, to aid the chemist in determining which functionalities may be present in an unknown compound. It is better to suggest more pasible functionalities, i.e., have possible false positive results, than to be unrealistically restrictive giving false negative interpretations. The chemist using MISIP or PAIRS should consider the interpretation results with this philosophy firmly in mind. PAIRS is available for distribution from the Quantum Chemistry Program Exchange, Bloomington, IN (Program number QCPE 426). MISIP is available as part of the user generated software from the Nicolet Instrument Corp. ACKNOWLEDGMENT
We acknowledge the contributionsof Graham Smith, Merck Sharp & Dohme Research Laboratories, for his valuable discussions and the staff of Nicolet Instrument Corp., especially Stephen Lowry, David Huppler, and Colleen Gilligan, for their technical support. LITERATURE CITED (1) Woodruff, H. B.; Smlth, 0. M. Anal. Chem. 1.980, 52, 2321-2327. (2) Woodruff, H. B.; Smith, 0. M. Anal. Chim. Acta W81, 133, 543-553. (3) Tomelllnl, S. A.; Sapersteln, D. D.; Stevenson, J. M.; Smith, G. M.; Woodruff, H. 8.; Seellg, P. F. Anal. Chem. 1981, 53, 2367-2369. (4) Weitl, D. “Infrared Vapour Spectra”; Heyden: New York, 1970. (5) Delaney, M. F.; Warren, V., Jr. Anal. Chem. 1981, 5 3 , 1460-1462.
RECEIVED for review April 11,1983. Accepted September 21, 1983.
