Photoinduced Structural Changes as the Factor Influencing the

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The photo-induced structural changes as the factor influencing the direction of the photochemical reaction in the crystal Krzysztof Konieczny, Julia B#kowicz, Renata Siedlecka, Tomasz Galica, and Ilona Turowska-Tyrk Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.6b01750 • Publication Date (Web): 30 Jan 2017 Downloaded from http://pubs.acs.org on January 30, 2017

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Crystal Growth & Design

The photoinduced structural changes as the factor influencing the direction of the photochemical reaction in the crystal Krzysztof Konieczny, Julia Bąkowicz, Renata Siedlecka, Tomasz Galica and Ilona Turowska-Tyrk* Faculty of Chemistry, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland Abstract The path of the Norrish-Yang reaction of methylammonium 4-(2,4,6triisopropylbenzoil)benzoate was studied by means of X-ray structure analysis. The following parameters influenced by this photochemical reaction were monitored: (a) intramolecular distances and angles in the reaction centre, (b) the size of the free space near the reactive atoms, (c) the mutual orientation of molecular fragments, (d) the cell parameters and (e) the product content. Product molecules were created in two modes, namely by the reaction of the 2-isopropyl or 6-isopropyl group, which has not been revealed previously for other 2,4,6triisopropylbenzophenones. The 2-isopropyl group took part in the photochemical reaction during the whole crystal transformation, whereas the reaction of the 6-isopropyl group started with a delay and ceased before the total crystal conversion. The reason for such behaviour was explained by the analysis of changes in the free space near both o-isopropyl groups with the crystal phototransformation.

Ilona Turowska-Tyrk Wybrzeże Wyspiańskiego 27 50-370 Wrocław, Poland Fax: +48 71 320 33 64 Email: [email protected]

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The photo-induced structural changes as the factor influencing the direction of the photochemical reaction in the crystal Krzysztof Konieczny, Julia Bąkowicz, Renata Siedlecka, Tomasz Galica and Ilona Turowska-Tyrk* Faculty of Chemistry, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland

Abstract

The

path

of

the

Norrish-Yang

reaction

of

methylammonium

4-(2,4,6-

triisopropylbenzoil)benzoate was studied by means of X-ray structure analysis. The following parameters influenced by this photochemical reaction were monitored: (a) intramolecular distances and angles in the reaction centre, (b) the size of the free space near the reactive atoms, (c) the mutual orientation of molecular fragments, (d) the cell parameters and (e) the product content. Product molecules were created in two modes, namely by the reaction of the 2-isopropyl or 6-isopropyl

group,

which has not been revealed previously for other 2,4,6-

triisopropylbenzophenones. The 2-isopropyl group took part in the photochemical reaction during the whole crystal transformation, whereas the reaction of the 6-isopropyl group started with a delay and ceased before the total crystal conversion. The reason for such behaviour was


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explained by the analysis of changes in the free space near both o-isopropyl groups with the crystal phototransformation.

Introduction A large group of compounds undergoing a Norrish-Yang reaction in crystals are derivatives of 2,4,6-triisopropylbenzophenone. For this group, twenty-two crystal and molecular structures were published.1-14 For ten compounds the structures containing product molecules are known.2,5,7,10-15 However, the path of this photochemical reaction in crystals of only five such compounds was monitored (refcodes CARGIM0n, n=1,2,3; HOJYAI; HOJYAI0n, n=1-8; DULJUQ; HOJYUC; HOJZAJ; HOJZEN; HOJZIR; SATQUZ01; UREZEN; UREZEN0n, n=15; URUYUC; URUYUC0n, n=1,2; USACOH; USACOH0n, n=1-4).10,11,13,15 In some of the above-mentioned studies the strong influence of a crystal lattice on the rate and of a NorrishYang reaction was emphasized. Such influence was evidenced quantitatively, for instance, in the case

of

benzylammonium,

pyrrolidinium

and

ammonium

4-(2,4,6-

triisopropylbenzoyl)benzoates13, where a crystal lattice was changed by introducing different counter-ions and in the case of benzylammonium 4-(2,4,6-triisopropylbenzoyl)benzoate where a crystal lattice was modified by high pressure.15 The role of a crystal lattice was also analysed for 2,4,6-triisopropylbenzophenones with two molecules in an asymmetric unit.10 The compound presented in this paper is a salt of 4-(2,4,6-triisopropylbenzoil)benzoic acid with

methylamine,

compound

1.

It

significantly

differs

from

other

2,4,6-

triisopropylbenzophenones, since both o-isopropyl groups take part in the formation of the product (2-isopropyl in one molecule and 6-isopropyl in another molecule). Both groups react at a different reaction rate and thus form different amounts of the product. In this paper, we will explain the reasons of such behaviour.


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Experimental 4-(2,4,6-Triisopropylbenzoyl)benzoic

acid

was

prepared

via

acylation

of

1,3,5-

triisopropylbenzene with 4-carbomethoxybenzoyl chloride followed by the basic hydrolysis of the obtained product, according to the literature procedure.16 An excess of methylamine (0.5 ml, 33% solution in abs. ethanol) was added to a solution of 4-(2,4,6-triisopropylbenzoyl)benzoic acid (47.5 mg, 0.135 mmol) in abs. ethanol (5 ml). The solution was left at room temperature for crystallization. After evaporation of the solvent, crystals of compound 1 were furnished. The Norrish-Yang reaction in the crystal of compound 1 was induced by irradiation with a 100 W Hg lamp equipped with a water filter and a BG39 glass filter. The glass filter transmitted wavelengths referring to the low-energy absorption tail and this helped to keep the crystal at good quality and to conduct the reaction homogenously.17,18 The transmittance for the applied filter was: 0% for 320 > λ > 620 nm, 55% for ~ 350 nm and 95% for ~ 460 nm. The experiments were conducted in the dark. The times of crystal irradiation were: 0, 5, 15, 25, 35, 45, 55, 65 and 85 min in total. After each irradiation data collection was carried out by means of a diffractometer equipped with a CCD detector and CrysAlisPro software.19 The unit cell parameters were determined after each UV irradiation. The quality of the X-ray data allowed for the determination of the crystal structures for 0, 5, 15, 35 and 85 min of UV irradiation. For the solution and refinement of the crystal structures, Shelxs and Shelxl software was applied.20,21 In the case of the crystal structure before UV irradiation, all non-hydrogen atoms were refined anisotropically. The positions of hydrogen atoms were found in a difference Fourier map,


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excluding the hydrogen atoms of methyl groups in the anion, which were positioned geometrically with Uiso=1.5Ueq of the respective carbon atoms. For the remaining structures characterized by a disorder, a set of restraints was used, namely DFIX, DANG, SIMU and FLAT.21 The C, O and N atoms in the major component were refined anisotropically and in the minor components were treated isotropically. The H atoms in the cation of the major component were refined as riding rotating groups and in the anion of the major and minor components as riding ones. The H atoms in the cation of the minor components and in the hydroxyl group of the anionic products were omitted. The reactant and product content was determined at the stage of the crystal structure refinement on the grounds of the site occupation factor (SOF). In order to provide additional evidence that both o-isopropyl groups of compound 1 are reactive, a further refinement was made for the crystal of the pure product, i.e. for the crystal after 85 min of UV irradiation. Namely, we assumed temporarily that in the crystal there are only product molecules formed by the reaction of the 2-isopropyl group and not by the reaction of the 6-isopropyl group. In such a situation the R1 value increased by 5.1 % (from 12.77% to 17.87%). The result of this procedure also indicates that both o-isopropyl groups create product molecules during the reaction. The selected crystallographic and experimental data, together with the reactant and product content in the crystal, are given in Table 1.

Results and discussion The reactant molecule of compound 1 contains two o-isopropyl groups and theoretically each of them can take part in a Norrish-Yang reaction. Certainly, in one molecule only one group has


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such a possibility. For reasons further discussion, we named the product formed by the 2isopropyl P and formed by the 6-isopropyl Z. The equation of this reaction is given in Scheme 1a. The molecular structures for various stages of the crystal phototransformation, including the ones for the pure reactant and pure product crystals are presented in Fig. 1. The product molecule is chiral with a chirality centre at atom C7. Nevertheless, because the crystal is centrosymmetric (space group I2/a) there are equal amounts of both enantiomers of the product in the crystal. Susceptibility of a molecule, and groups within it, to a Norrish-Yang reaction can be described by means of five geometrical parameters. Their definition is given in Scheme 1b.22-24 The values of these parameters for compound 1, as well as the literature ranges and the ideal values, are presented in Table 2. As can be seen, for the 2-isopropyl group, which takes part in the formation of the P product, the values of d and Θ are worse, i.e. farther from ideal, than for 6-isopropyl which is active in the formation of the Z product. The values of the remaining parameters are very similar for both groups. The above indicates that the reactivity of the 6-isopropyl group should be higher. Nevertheless, it originates from our studies described in this paper that the situation is reverse: 6-isopropyl does not react at the beginning of the crystal phototransformation and later it reacts much slower than 2-isopropyl. It results from the above that other factors influencing the reactivity of the studied compound should exist. This topic will be discussed below. The increase of the P and Z product content in the crystal along with the time of UV irradiation is shown in Fig. 2. It should also be emphasized that the values of d and Θ for the 2-isopropyl group exceed the ranges recognised by present scientific literature. Such values should imply photochemical inertia of this group, however, this is not the case. According to the results of the studies of


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compound 1, we suggest to enlarge the known literature ranges and to use new ones (see Table 2). In order to explain the reasons of the unexpected reactivity of the 2-isopropyl and 6-isopropyl groups, we analysed the size and shape of free space around both groups. The analysis of the free space in the crystal before the reaction, i.e. when there are only reactant molecules in the crystal, shows that there is a big free space of 9.0(2) Å3 near the 2isopropyl group. This is shown in Fig. 3a. The volume of the free space was calculated by means of the Platon software.27 However, the situation changes when there are also molecules of the P product in the crystal, except for reactant molecules. In these circumstances reactant molecules have a different surrounding. We can imagine two border situations: (a) a reactant molecule is surrounded by other reactant molecules and (b) a reactant molecule is surrounded by product molecules. The former is more probable at the initial stages of the reaction. We artificially created the lattices corresponding to both of the above situations for the first step of the irradiation of the crystal, i.e. for the crystal irradiated during 5 min and containing ca. 8% of the P product. It occurred that when near a reactant molecule there are only other reactant molecules then, as a consequence, the free space is similar to the one in the non-irradiated crystal, namely its volume is 7.0(1) Å3, and this is favourable for the formation of the P product and unfavourable for the formation of the Z product. However, when near a reactant molecule there are only molecules of the P product, then there is also a large free space near the 6isopropyl group and its size is comparable with the size of the void near the 2-isopropyl group. The volume of the void is 14.0(8) Å3 and 17.0(8) Å3 near the 2-isopropyl and 6-isopropyl group, respectively. This is shown in Fig. 3b & 3c. According to this, both P and Z product molecules can be formed. Our studies show that the presence of molecules of the P product is the factor


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having crucial influence on the formation of molecules of the Z product. Because of this, Z molecules are observed in the crystal after the next step of UV irradiation, however, their amount is rather low, since the population of the P product is low. After some time the amount of molecules of the Z product becomes constant, while molecules of the P product are still being formed (see Figure 2). Searching for the reasons of this fact, we analysed the free space near the o-isopropyl groups and also the intramolecular geometrical parameters describing molecular susceptibility to the Norrish-Yang reaction. Similarly, as above, we created fragments of the lattice where one reactant molecule was only surrounded by (a) reactant molecules, (b) molecules of the P product and (c) molecules of the Z product. The comparison of the free space near the 2-isopropyl and 6-isopropyl groups revealed that the formation of the P product is favourable in all the situations. When a reactant molecule is surrounded by other reactant molecules, there is a big free space near the 2-isopropyl group only and its volume is 13.0(5) Å3. A similar situation is observed when a reactant molecule is surrounded by Z product molecules, then a free space is also present near 2-isopropyl only and its volume is 28(2.5) Å3. In the third considered case, i.e. when a reactant molecule is surrounded by P product molecules, free spaces are observed in the vicinity of both o-isopropyl groups. Nevertheless, the free space near 2-isorpopyl is more than twice larger than that near 6isopropyl: 18.0(7) Å3 and 8.0(1) Å3 for 2- and 6-isopropyl, respectively. Another reason for the observed differences in the reactivity of both o-isopropyl groups might also be the distance between the carbon atoms taking part in the reaction and creating the cyclobutene ring, D, which at this stage of the crystal phototransformation is 2.78(5) and 2.87(5) Å for 2-isopropyl (product P) and 6-isopropyl (product Z), respectively. Both values indicate that P and Z could be created, but the situation is more suitable for the formation of P.


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Along with the reaction progress the geometry of reactant molecules change, especially in the reaction centre: for instance the D distance for both o-isopropyl groups, which is shown in Fig. 4a. As can be seen, for 2-isopropyl D is constant at the beginning of the crystal phototransformation and afterwards decreases by 0.17(5) Å, which is statistically significant, and for 6-isopropyl D is statistically constant during the whole reaction. In scientific literature there are known compounds undergoing a Norrish-Yang reaction and for which D changes in one of the above manners.11,15,28,29 The relationships described in the literature were interpreted as being a result of some stress of product molecules imposed on reactant molecules, which is stronger for a larger population of product molecules.11,15,28,29 The same interpretation can be applied in the case of compound 1. Since after 35 min of UV irradiation, the P product is the major component in the crystal (64.8%), the geometry of reactant molecules accommodates to the geometry of molecules of the P product. According to this rule the D distance decreases for 2-isopropyl (i.e. on the side of a reactant molecule where a cyclobutene ring is created in P molecules) and does not for the 6-isopropyl group. During the Norrish-Yang reaction of compound 1 the orientation of whole molecules and their fragments also changes. For instance, the dihedral angle between two benzene rings alters from 87.7(4)° to 76.9(19)°, which is shown in Fig. 4b. It is worth emphasizing that the mutual orientation of the respective rings in molecules of the P product in the pure product crystal is 76.6(5)°, which again shows that reactant molecules accommodate to the major product lattice. All the changes proceeding in the crystal and described above are reflected in the variations in the unit cell parameters, which are presented in Fig. 5. The biggest of them are observed for parameter c, which increases by 2.43(2) Å, i.e. 5.4%. Parameter a decreases by 0.861(10) Å, i.e. 5.0% and parameter b decreases only slightly, namely by 0.048(3) Å, i.e. 0.8%. As can be seen


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from the figure, the biggest changes are observed in the range between 15 and 35 min and the Norrish-Yang reaction seems to be completed after 45 min of UV irradiation.

Conclusions The salt of 4-(2,4,6-triisopropylbenzoil)benzoic acid with methylamine, compound 1, undergoes the Norrish-Yang reaction in crystals. The changes in the molecular and crystal geometry brought about by this photochemical reaction and the changes in the direction of this reaction were presented and discussed. At the beginning of the crystal phototransformation only the 2-isopropyl group takes part in the reaction, afterwards both o-isopropyl groups create product molecules and at the end of the phototransformation the reactivity of 6-isopropyl group is ceased and again the product is only created by the 2-isopropyl group. The reason for the formation of two kinds of product molecules, P and Z, and the reason for the differences in reactivity of both o-isopropyl groups were explained by means of the significant changes in the size of the free space near the o-isopropyl groups along with the crystal phototransformation. To the best of our knowledge this is the first example of monitoring a reaction path when a product is formed in two modes. It was also noticed that the changes in the geometry of reactant molecules, for instance, in the distance between the reactive carbon atoms and in the mutual orientation of molecular fragments, are a result of adaptation of reactant molecules to the lattice of the major product.

ACKNOWLEDGMENT This work was financed by the statutory activity subsidy from the Polish Ministry of Science and Higher Education for the Faculty of Chemistry of the Wroclaw University of Technology.


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ASSOCIATED CONTENT Accession Codes CCDC 1520028-1520032 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033. AUTHOR INFORMATION Corresponding Author *Email: [email protected] Funding Sources The Polish Ministry of Science and Higher Education Notes The authors declare no competing financial interest.

REFERENCES (1) Koshima, H.; Maeda, A.; Masuda, N.; Matsuura, T.; Hirotsu, K.; Okada, K.; Mizutani, H.; Ito, Y.; Fu, T.Y.; Scheffer, J.R.; Trotter, J. Tetrahedron: Asymm. 1994, 5, 1415-1418. (2) Hirotsu, K.; Okada, K.; Mizutani, H.; Koshima, H.; Matsuura, T. Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A 1996, 277, 99-106. (3) Fu, T.Y.; Scheffer, J.R.; Trotter, J. Acta Crystallogr., Sect. C: Struct. Chem. 1997, 53, 1259-1262.


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(4) Fukushima, S.; Ito, Y.; Hosomi, H.; Ohba, S. Acta Crystallogr., Sect. B: Struct. Sci. 1998, 54, 895-906. (5) Hosomi, H.; Ito, Y.; Ohba, S. Acta Crystallogr., Sect. B: Struct. Sci. 1998, 54, 907-911. (6) Koshima, H.; Kawanishi, H.; Nagano, M.; Yu, H.; Shiro, M.; Hosoya, T.; Uekusa, H.; Ohashi, Y. J. Org. Chem. 2005, 70, 4490-4497. (7) Koshima, H.; Fukano, M.; Uekusa, H. J. Org. Chem. 2007, 72, 6786-6791. (8) Koshima, H.; Ide, Y.; Fukano, M.; Fujii, K.; Uekusa, H. Tetrahedron Lett. 2008, 49, 43464348. (9) Ito, Y.; Takahashi, H.; Hasegawa, J.; Turro, N.J. Tetrahedron 2009, 65, 677-689. (10) Bąkowicz, J.; Turowska-Tyrk, I, Acta Crystallogr., Sect. C: Struct. Chem. 2010, 66, o29– o32. (11) Bąkowicz, J.; Skarżewski, J.; Turowska-Tyrk, I. CrystEngComm 2011, 13, 4332–4338. (12) Fujii, K.; Uekusa, H.; Fukano, M.; Koshima, H. CrystEngComm 2011, 13, 3197-3201. (13) Bąkowicz, J.; Olejarz, J.; Turowska-Tyrk, I. J. Photochem. Photobiol., A: Chem. 2014, 273, 34–42. (14) Koshima, H.; Fukano, M.; ,Ojima, N.; Johmoto, K.; Uekusa, H.; Shiro, M. J. Org. Chem. 2014, 79, 3088-3093. (15) Konieczny K.; Bąkowicz J.; Turowska-Tyrk I. CrystEngComm 2015, 17, 7693–7701. (16) Ito, Y.; Kano, G.; Nakamura, N. J. Org. Chem. 1998, 63, 5643-5647.


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(17) Enkelmann, V.; Wegner, G.; Novak, K.; Wagener, K.B. J. Am. Chem. Soc. 1992, 115, 10390–10391. (18) Novak, K.; Enkelmann, V.; Wegner, G.; Wagener, K.B. Angew. Chem. Int. Ed. Engl. 1993, 32, 1614–1616. (19) Rigaku Oxford Diffraction, (2016), CrysAlisPro Software system, Version 1.171.38.41, Rigaku Corporation, Oxford, UK (20) Sheldrick, G.M. Acta Crystallogr. Sect. A: Found. Crystallogr. 2008, 64, 112–122. (21) Sheldrick, G.M. Acta Crystallogr. Sect. C: Struct. Chem. 2015, 71, 3–8. (22) Ihmels, H.; Scheffer, J. R. Tetrahedron 1999, 55, 885–907. (23) Natarajan, A.; Mague, J.T.; Ramamurthy, V. J. Am. Chem. Soc. 2005, 127, 3568–3576. (24) Xia, W.; Scheffer, J. R.; Botoshansky, M.; Kaftory, M. Org. Lett. 2005, 7, 1315–1318. (25) Farrugia, L.J. J. Appl. Crystallogr. 2012, 45, 849–854. (26) Macrae, C.F.; Edgington, P.R.; McCabe, P.; Pidcock, E.; Shields, G.P.; Taylor, R.; Towler, M.; van de Streek, J. J. Appl. Crystallogr. 2006, 39, 453–457. (27) Spek, A.L. Acta Crytsllogr. Sect. D: Biol. Crystallogr. 2009, 65, 148-155. (28) Turowska-Tyrk, I.; Trzop, E.; Scheffer, J.R.; Chen, S. Acta Crystallogr. Sect. B: Struct. Sci. 2006, 62, 128-134. (29) Turowska-Tyrk, I.; Bąkowicz, J.; Scheffer, J.R. Acta Crystallogr. Sect. B: Struct. Sci. 2007, 63, 933-940.


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Scheme 1. (a) The equation of the Norrish-Yang reaction for compound 1 and (b) the graphical representation of five geometrical parameters describing susceptibility to the Norrish-Yang reaction. Table 1. The crystal and experimental data. 0 min

5 min

15 min

35 min

85 min

Reactant content/%

100

91.2(4)

68.0(3)

16.9(3)

0

P product content/%

0

8.8(4)

24.9(3)

64.8(3)

81.9(8)

Z product content/%

0

0

7.1(3)

18.3(3)

18.1(8)

Chemical formula

C24H33O3N

C24H33O3N

C24H33O3N

C24H33O3N

C24H33O3N

Formula weight

383.52

383.52

383.52

383.52

383.52

Crystal dimensions

0.55 x 0.18 x 0.10

0.55 x 0.18 x 0.10

0.55 x 0.18 x 0.10

0.55 x 0.18 x 0.10

0.55 x 0.18 x 0.10

Crystal system

Monoclinic

Monoclinic

Monoclinic

Monoclinic

Monoclinic

Space group

I2/a

I2/a

I2/a

I2/a

I2/a

a/Å

17.1387(10)

17.0887(12)

16.887(3)

16.252(5)

16.278(10)

b/Å

6.3047(4)

6.3109(4)

6.3256(10)

6.2836(16)

6.257(3)

c/Å

44.649(3)

44.701(4)

45.157(9)

46.864(12)

47.08(2)

98.744(6)

98.798(7)

98.743(19)

99.12(3)

99.07(5)

V/Å

4768.4(5)

4764.1(6)

4767.6(15)

4725(2)

4735(4)

Z

8

8

8

8

8

Dx/Mg m-3

1.068

1.069

1.069

1.078

1.076

µ/mm-1

0.069

0.069

0.069

0.070

0.070

T/K

299

299

299

299

299

Reflections collected

8533

8327

7371

7201

7358

Reflections independent

4678

4210

3743

3703

3711

Reflections observed

2707

3205

2497

1965

1528

Rint

0.024

0.024

0.071

0.071

0.103

R, wR (F >2σ(F )), S

0.062, 0.159, 1.02

0.072, 0.173, 1.14

0.129, 0.287, 1.11

0.161, 0.386, 0.87

0.128, 0.345, 1.08

∆ρmax, ∆ρmin/eÅ-3

0.17, -0.17

0.18, -0.15

0.18, -0.17

0.23, -0.22

0.27, -0.19

β/° 3

2

2

Table 2. The values of the geometrical parameters describing susceptibility to a Norrish-Yang reaction. d [Å] Compound 1, 2-isopropyl 3.07

D [Å]

Θ [°]

∆ [°]

ω [°]

2.920(4)

104.3

53.4

83.4


14

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Compound 1, 6-isopropyl 2.89

2.931(4)

115.0

54.6

83.4

180

0

90-120

Ideal values

< 2.7

Literature rangea

2.39-2.95

2.82-3.12

112.0-131.6 50.8-85.5

52.0-88.0

New literature rangeb

2.39-3.07

2.82-3.12

104.3-131.6 50.8-85.5

52.0-88.0

a b

Bąkowicz et al., 201414 this paper

Figure 1. The chemical species for the crystal containing (a) 100% of the reactant, i.e. before the UV irradiation (b) 91.2% of the reactant and 8.8% of the P product, i.e. after 5 min of the UV irradiation (c) 16.9% of the reactant, 64.8% of the P product and 18.3% of the Z product, i.e. after 35 min of the UV irradiation and (d) 81.9% of the P product and 18.1% of the Z product, i.e. after 85 min of the UV irradiation. The atomic displacement parameters were drawn at a 20% probability level for plots (a), (b) and (d) and at a 10% probability level for (c).25 For clarity hydrogen atoms were omitted in plots (b)-(d). Figure 2. The product content in the crystal versus the time of UV irradiation (the P product circles, the Z product - triangles and the product in total - squares). Figure 3. (a) The lattice and the free space in the crystal containing 100% of reactant molecules, i.e. before UV irradiation. The crystal lattice and the free space was calculated with the assumption that one reactant molecule was surrounded (b) only by reactant molecules and (c) only by P product molecules in the crystal containing 91.2% of the reactant and 8.8% of the P product. The voids were calculated by means of Mercury software26 for the ball radius 1.0 Å and the grid 0.2 Å.


15


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Figure 4. (a) The changes in the D distance with the time of UV irradiation for 2-isopropyl (black) and 6-isopropyl (red). (b) The variations in the angle between the planes of two benzene rings of the reactant molecule, C1→C6 and C8→C13, along with the time of UV irradiation. Figure 5. The variations in the unit cell parameters with the time of UV irradiation.


16

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For Table of Contents Use Only, The photo-induced structural changes as the factor influencing the direction of the photochemical reaction in the crystal, Krzysztof Konieczny, Julia Bąkowicz, Renata Siedlecka, Tomasz Galica and Ilona TurowskaTyrk

Why do molecules react in different modes at different stages of the photochemical reaction?


17


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Figure 1. The chemical species for the crystal containing (a) 100% of the reactant, i.e. before the UV irradiation (b) 91.2% of the reactant and 8.8% of the P product, i.e. after 5 min of the UV irradiation (c) 16.9% of the reactant, 64.8% of the P product and 18.3% of the Z product, i.e. after 35 min of the UV irradiation and (d) 81.9% of the P product and 18.1% of the Z product, i.e. after 85 min of the UV irradiation. The atomic displacement parameters were drawn at a 20% probability level for plots (a), (b) and (d) and at a 10% probability level for (c).25 For clarity hydrogen atoms were omitted in plots (b)-(d). 184x420mm (600 x 600 DPI)


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Figure 2. The product content in the crystal versus the time of UV irradiation (the P product - circles, the Z product - triangles and the product in total - squares). 61x46mm (600 x 600 DPI)



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Figure 3. (a) The lattice and the free space in the crystal containing 100% of reactant molecules, i.e. before UV irradiation. The crystal lattice and the free space was calculated with the assumption that one reactant molecule was surrounded (b) only by reactant molecules and (c) only by P product molecules in the crystal containing 91.2% of the reactant and 8.8% of the P product. The voids were calculated by means of Mercury software26 for the ball radius 1.0 Å and the grid 0.2 Å. 159x157mm (600 x 600 DPI)


Page 20 of 23

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Figure 4. (a) The changes in the D distance with the time of UV irradiation for 2-isopropyl (black) and 6isopropyl (red). (b) The variations in the angle between the planes of two benzene rings of the reactant molecule, C1→C6 and C8→C13, along with the time of UV irradiation. 127x198mm (600 x 600 DPI)



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Figure 5. The variations in the unit cell parameters with the time of UV irradiation. 195x476mm (600 x 600 DPI)


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Scheme 1. (a) The equation of the Norrish-Yang reaction for compound 1 and (b) the graphical representation of five geometrical parameters describing susceptibility to the Norrish-Yang reaction. 92x106mm (600 x 600 DPI)


Photoinduced Structural Changes as the Factor Influencing the

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