The Reasons for Different Kinetics of the Norrish-Yang Reaction in Crystals. Structural and Spectroscopic Studies

Article abstract of DOI:10.1021/acs.cgd.0c00245

The kinetics of the photochemical Norrish-Yang reaction in single crystals was studied using the example of 1,3,5,7-tetraazatricyclo[3.3.1.13,7]decane 4-(2,4,6-triisopropylbenzoyl)benzoate by X-ray diffraction and Raman spectroscopy. The reaction in the studied compound proceeds in two stages described by the Johnson-Mehl-Avrami-Kolmogorov model. In the first stage the reaction progresses homogeneously at a constant rate, but for the second mode, which started at ca. 50% conversion, the reaction progresses with autoinhibition. The reasons for this autoinhibition are (i) the changes in the geometry of the reaction center during the second stage, which were not observed in the first stage, (ii) the C-H···πinteractions, which become stronger along with the reaction progress, and (iii) the change in character of the carboxylate group toward the carboxylic-like group. The Norrish-Yang reaction also proceeds in crystals at 0.2 GPa, as stated on the grounds of the characteristic changes in the unit cell parameters along with UV irradiation.

Full text of DOI:10.1021/acs.cgd.0c00245

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Article
The Reasons for Different Kinetics of the Norrish-Yang Reaction in
Crystals. Structural and Spectroscopic Studies
Krzysztof A. Konieczny,* Anna Szczurek, Julia Bąkowicz, Renata Siedlecka, Arkadiusz Ciesielski,
́
Michał K. Cyranski, and Ilona Turowska-Tyrk*
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ABSTRACT: The kinetics of the photochemical Norrish-Yang
reaction in single crystals was studied using the example of 1,3,5,7-
tetraazatricyclo[3.3.1.13,7]decane 4-(2,4,6-triisopropylbenzoyl)-
benzoate by X-ray diffraction and Raman spectroscopy. The
reaction in the studied compound proceeds in two stages described
by the Johnson-Mehl-Avrami-Kolmogorov model. In the first stage
the reaction progresses homogeneously at a constant rate, but for the second mode, which started at ca. 50% conversion, the reaction
progresses with autoinhibition. The reasons for this autoinhibition are (i) the changes in the geometry of the reaction center during
the second stage, which were not observed in the first stage, (ii) the C−H···π interactions, which become stronger along with the
reaction progress, and (iii) the change in character of the carboxylate group toward the carboxylic-like group. The Norrish-Yang
reaction also proceeds in crystals at 0.2 GPa, as stated on the grounds of the characteristic changes in the unit cell parameters along
with UV irradiation.
Scheme 1. Norrish-Yang Reaction (Path 1) and the Yang
Cyclization to a Five-Membered Ring (Path 2)
INTRODUCTION
■
During the Norrish-Yang reaction an achiral reactant molecule
transforms into a chiral photoproduct molecule. The
accomplishing of reactions in an enantioselective way is one
of the challenges in organic chemistry. Since the Norrish-Yang
reaction in a crystalline state can be conducted in a more
controlled manner than in solution, it attracts the interest of
many organic chemists.1−8 Its advantage over reactions
conducted in solutions is mainly connected with the possibility
to correlate chemical behavior (kinetics, stereochemistry) with
a crystal structure. It is worth adding that the reaction in a
crystalline state can proceed differently than in solutions owing
to different geometrical parameters for both media. The
Norrish-Yang reaction is a photochemical process that takes
place in compounds having a carbonyl group and a γ-hydrogen
atom and that leads to a four-membered ring through a 1,4-
biradical (Scheme 1, path 1). The formation of the 1,4-
biradical is named the Norrish type II reaction, and the
recombination leading to the ring is known as the Yang
cyclization.9 In special cases, when except for γ-hydrogen there
is δ-hydrogen in a molecule, it is possible that a 1,5-biradical
and afterward a five-membered ring is formed (Scheme 1, path
2). There are known cases when only one type of ring or
simultaneously both types of them are obtained in one
crystal.7,10
considered. This geometry can be described by five
parameters: d, D, Δ, θ, and ω.11,12 Below they are presented
for the case of the Norrish-Yang reaction (Scheme 2):
• dthe distance between the γ-hydrogen and carbonyl
oxygen atoms; the ideal value is less than 2.7 Å.11
• Dthe distance between two carbon atoms forming the
new covalent bond; the ideal value is less than 3.2 Å.12
Received: February 25, 2020
Revised: July 9, 2020
Published: July 9, 2020
The fact as to whether the ring is formed, and which of the
two above-mentioned rings (four-membered or five-mem-
bered) occurs, depends on several factors. Among the most
crucial, the geometry of the reaction center must be
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reaction cavity analyzed but also elasticity compensating strains
caused by a reaction and protecting crystals from crack-
ing.42−46 The feedback was the factor responsible for kinetics
in the case of various compounds.43,44,47−50 Sometimes the
analysis of one or several individual intermolecular contacts
provided valuable information connected to the proceeding
photochemical reactions in crystals. For instance, hydrogen
bonds were given as the reason for photochemical inertia51−53
or activity.18,54 π···π interactions had a positive influence on
reactivity by preorientating molecules in crystals55,56 or a
negative impact by impeding atomic shifts.20,57
Scheme 2. Graphical Representation of the Geometrical
Parameters Describing Susceptibility to the Norrish-Yang
Reaction
The above-described factors are connected with internal
crystal structures. It should be added that, except for these,
there are other factors, which are external, such as radiation
wavelength, temperature, and pressure.59
The kinetics of a photochemical reaction in a crystal can be
described in terms of the Johnson-Mehl-Avrami-Kolgomorov
(JMAK) model by the following equation:58,60
• Δthe CO···H angle between the atoms of the
carbonyl group and γ-hydrogen; the ideal value is 90°−
120°.11
• θthe C−H···O angle between γ-carbon, γ-hydrogen,
and carbonyl oxygen; the ideal value is 180°.13
P = 1 − exp(−kt)n
where:
P is product content.
k is reaction rate.
t is time.
• ωthe torsion angle describing the deviation of the γ-
hydrogen from the plane of the carbonyl group; the ideal
value is 0°.14
The above-given ideal values are also valid in the case of the
formation of a five-membered ring, except for the value of
parameter D, which in such a situation should be less than 3.4
Å.15
n is the Avrami exponent.
The n parameter provides the information about dimension-
ality of product growth D. For n equal to 2, 3, or 4 the
formation of product proceeds in 1, 2, or 3 dimensions,
respectively. In the case when n is 1, there are no vectors of
product propagation, and product molecules occur independ-
ently and randomly. In such a situation, domains that could
cause undesirable phase separation are not formed, and a
reaction is homogeneous. It should be mentioned that certain
circumstances arose in which the values of the Avrami
exponent were significantly different from integers.61,62 In
practice the logarithmic form of the JMAK equation, known as
the Avrami plot, is used. The linear dependence between
ln[−ln(1 − P)] and ln t justifies the use of the model.
The JMAK model was applied to photochemical reactions
such as the [2 + 2] photodimerization of α-trans-cinnamic,61,63
β-cinnamic,64 o-methoxycinnamic, and o-ethoxycinnamic
acids65 and the [4 + 4] photodimarization of 9-anthracene-
carboxylic acid.66 It was also used for the description of the
kinetics of the Norrish-Yang reaction in crystals of ammonium
and benzylaminium 4-(2,4,6-triisopropylbenzoyl)benzoates.
The analyses performed revealed a homogeneous mechanism
with autoinhibition for the ammonia salt, n = 0.84, and a
hybrid mechanism (homogeneous and one-directional) for the
benzylamine salt, n = 1.44(4).18 A very interesting phenom-
enon was met in the case of the benzylidene oxazolone
derivative, where the kinetics significantly changed at a certain
stage of the process, as it was evidenced by two straight lines
having different slopes in the Avrami plot. During the first
stage, the reaction was homogeneous, n = 1.1(2), and during
the second one it proceeded homogeneously with auto-
inhibition, n = 0.33(6). The observed autoinhibition was
connected with certain, yet gradual, degradation of a crystal.67
In this paper, we aim to reveal and explain on structural
grounds the differences in the unique kinetics of the Norrish-
Yang reaction in crystals in the case of 1,3,5,7-tetraazatricyclo-
[3.3.1.13,7]decane 4-(2,4,6-triisopropylbenzoyl)benzoate by
means of X-ray diffraction and additionally by Raman
spectroscopy.
At times, the analysis of parameter d only enabled the
rationalization of photochemical reactivity in crystals, as it was
in the case of the Yang cyclization of α-1-norbornylacetophe-
none derivatives.2,8 The analysis of d and Δ explained the
predominant formation of a five-membered ring (not four-
membered) for phenylethaneaminium 4-(2,4,6-
triisopropylbenzoyl)benzoate.7
Nevertheless, there were also cases when the analysis of all
five parameters provided valuable results, for instance, when
explaining why only one of two o-isopropyl groups was
reactive6,16−18 and why there were differences in the reactivity
of three salts of 4-(2,4,6-triisopropylbenzoyl)benzoic acid.18
However, there were cases where the analysis of the
geometrical parameters merely explained the occurrence of
the reaction but did not provide the answer as to why only one
of the two fragments having a similar geometry took part in the
reaction.19 In terms of the geometrical demands for
benzophenones, the role of the dihedral angle between a
carbonyl group and a benzene ring was also emphasized.20
According to the topochemical postulate, a photochemical
reaction proceeds in crystals when there is the possibility of
breaking old bonds and forming new ones. Such a reaction is
easier when the required atomic shifts are small and a reaction
cavity21−27 does not significantly change its geometry.28,29
However, when there is free space close to the reacting
molecular fragments, the reaction can occur, although the
necessary shifts and changes are significant. Moreover, the
existence of such a free space can cause a crystal lattice to
better accommodate a strain caused by the appearance of
product molecules. The analysis of the size and shape of a
reaction cavity helped to explain the photochemical reactivity
of many compounds.22,24−27,30−32 It was reported that a big
reaction cavity of suitable shape facilitated a photochemical
reaction33−35 and a small cavity of unsuitable shape disabled a
reaction.20 The geometry of a reaction cavity was responsible
for the reaction rate,36−40 the reaction direction, and the
obtained products.5,19,41 Not only was the geometry of a
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Table 1. Experimental Data for the Selected Structures
pressure
0.1 MPa
0.1 MPa
0.1 MPa
0.2 GPa
product content/%
chemical formula
formula weight, g/mol
0
48.1(8)
C29H40N4O3
492.65
100
C29H40N4O3
492.65
0
C29H40N4O3
492.65
C29H40N4O3
492.65
crystal system, space group monoclinic, P21/c
monoclinic, P21/c
monoclinic, P21/c
monoclinic, P21/c
a, b, c, Å
26.6710(13), 8.6190(5),
26.308(2), 8.7899(7),
11.9218(8)
93.491(6)
2751.7(4)
4
25.8752(12), 9.0770(4),
11.8468(5)
94.268(4)
2774.7(2)
4
26.50(2), 8.5258(8),
11.7775(11)
92.72(2)
2658(2)
4
11.8835(6)
92.660(5)
2728.8(2)
4
β, deg
V, Å3
Z
Dx, Mg/m3
μ, mm−1
1.199
0.078
1.189
0.078
1.179
0.077
1.231
0.080
crystal size, mm
temperature, K
completeness, %
No. of reflections
No. of independent
reflections
0.60 × 0.40 × 0.03
295(2)
100
10 655
5640
0.60 × 0.40 × 0.03
295(2)
100
18 479
5417
0.60 × 0.40 × 0.03
295(2)
100
18 056
5460
0.40 × 0.36 × 0.04
295(2)
31.3
13 325
1504
No. of observed reflections
Rint
3699
0.026
3105
0.040
2374
0.065
717
0.194
R1 [F2 > 2σ(F2)]
wR2 [F2 > 2σ(F2)]
S
0.058
0.117
1.029
0.16, −0.19
0.053
0.117
1.030
0.16, −0.15
0.064
0.136
1.000
0.21, −0.16
0.085
0.203
1.020
0.17, −0.15
ρmax, ρmin, e Å−3
determined on the grounds of the site occupation factor. The selected
experimental data are gathered in Table 1, and the full data for all
structures are given in the cif files (see the Supporting Information).
The Raman spectra for crystal 1 before and after different periods
of UV exposure were recorded using a dispersive spectrometer
(LabRAMHR800 Horiba Jobin Yvon) equipped with a He−Ne laser
operated at 633 nm. The measurements were conducted for a 4000−
100 cm−1 range and spectral resolution of 2.5 cm−1. For a comparison
of the spectra, the intensities of the bands were normalized in relation
to the band at 1600 cm−1 resulting from a CC aromatic ring stretching
mode.
EXPERIMENTAL SECTION
■
4-(2,4,6-Triisopropylbenzoyl)benzoic acid was prepared by the
acylation of 1,3,5-triisopropylbenzene with 4-carbomethoxybenzoyl
chloride followed by the basic hydrolysis of the obtained product,
according to the procedure in the literature.68 To form the salt, the
stoichiometric amount of 1,3,5,7-tetraazatricyclo[3.3.1.13,7]decane
(urotropine) was added to 4-(2,4,6-triisopropylbenzoyl)benzoic acid
dissolved in ethanol. The crystals suitable for X-ray diffraction
experiments were obtained after recrystallization from a mixture of
ethanol and toluene (v/v 5:1).
Two crystals at ambient pressure (crystals 1 and 2) and one crystal
at 0.2 GPa (crystal 3) were examined. Crystal 2 was studied to
compare the kinetics of the Norrish-Yang reaction with that in crystal
1. The high-pressure data were collected using a Boehler-Almax
diamond anvil cell (DAC).69 Quartz was used as a high-pressure
sensor according to the method developed by Angel et al.,70 and
glycerine was used as a hydrostatic pressure medium. The
photochemical reaction was induced by means of a 100 W Hg
lamp equipped with a water filter and a BG-39 glass filter. Crystal 1
was irradiated for 5, 10, 20, 40, 60, 90, 160, 280, and 460 min, crystal
2 for 20, 40, and 80 min, and crystal 3 for 5, 10, and 20 min in total.
Before the irradiation, and after each of them, X-ray data were
collected. The crystal structures were determined by means of
SHELXS, SHELXT, and SHELXL71−73 implemented in Olex274 for
crystals 1 and 2 for all irradiation times except crystal 1 after 60 min of
irradiation and for crystal 3 before irradiation.
For pure reactant crystals 1 and 2, all non-hydrogen atoms were
refined anisotropically. For the structures containing both the reactant
and the product, the atoms in the carbonyl, hydroxyl, and reactive o-
isopropyl groups and in ring C8 → C13 were refined independently
for the reactant and the product, but the positions of the remaining
atoms were kept the same for both components. The atoms of the
major component were refined anisotropically, and isotropically they
were refined for the minor one. In all structures the hydrogen atoms
were positioned geometrically and treated as riding, except the
hydroxyl hydrogen, which was omitted in the partly reacted crystals
and the hydrogen at N1 forming the hydrogen bond with the 4-(2,4,6-
triisopropylbenzoyl)benzoate anion, which was refined freely in the
case of crystal 1. For the disordered structures DFIX, DANG, SIMU,
and occasionally FLAT restraints were used. The product content was
RESULTS AND DISCUSSION
■
1,3,5,7-Tetraazatricyclo[3.3.1.13,7]decane 4-(2,4,6-
triisopropylbenzoyl)benzoate undergoes the Norrish-Yang
reaction in a crystalline state. Of two potentially reactive o-
isopropyl groups, 2-isopropyl only takes part in the formation
of the product, which is presented in Figure 1a−c. As can be
seen in this figure, the product molecule does not significantly
change its position with respect to the reactant molecule. The
shifts of atoms are only observed for the reactive 2-isopropyl
group, carbonyl group, and aromatic ring C8 → C13. There
are two main kinds of factors supporting the reactivity of 2-
isopropyl: (i) the values of the geometrical intramolecular
parameters in the region of this group, suitable for the Norrish-
Yang reaction, and (ii) the volume of the void adjacent to it,
allowing shifts of atoms during the reaction. The values of the
intramolecular geometrical parameters for both o-isopropyl
groups, together with the ideal and literature ranges, are
presented in Table 2, and the voids can be seen in Figure 1d,e.
Evidently, for 2-isopropyl the values of these parameters are
closer to the ideal ones, and the void is relatively large. The
geometry for 6-isopropyl is less favorable for the Norrish-Yang
reaction, and there is no free space of a suitable size and shape
near this group.
The relationship between the product content and the
irradiation time is shown in Figure 2a,b for crystals 1 and 2.
Since we determined the crystal structures for many stages of
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Figure 1. ORTEP75 view of (a) the reactant molecule in the pure reactant crystal, (b) the reactant and product molecules for 48.1% reaction
progress, and (c) the product molecule in the pure product crystal together with the atom labels. The atomic displacement ellipsoids were drawn at
a 20% probability level. The free space around the reactant molecule at (d) ambient pressure and (e) 0.2 GPa (the void near 2-isopropyl shown by
the arrow). The radius of the ball localizing the free space was 0.9 Å, and the grid spacing was 0.2 Å.76
Table 2. Geometrical Reactivity Parameters for o-Isopropyl Groups of the Studied Compound
a
d [Å]
2.67
3.10
2.7
3.1
D [Å]
ω [deg]
Δ [deg]
θ [deg]
122.9
114.7
123
115
180
free space [Å3]
0.1 MPa
0.2 GPa
2-isopropyl
6-isopropyl
2-isopropyl
6-isopropyl
2.934(3)
2.955(3)
2.99(2)
2.91(1)
<3.2
75.5
87.0
73
88
64.8
48.1
67
46
90−120
46.8−88.0
16.0(4)
0
14.0(3)
0
ideal
literature range
<2.7
2.39−3.15
0
b
2.82−3.12
50.8−86.0
104.3−145.0
The radius of the ball localizing the free space was 0.9 Å, and the grid spacing was 0.2 Å.76 On the basis of the search in Cambridge Structural
a
b
Database, ver. 1.19.77
the reaction, including the structures before the reaction and
after 100% conversion, we were able to study the reaction
kinetics in detail by means of the Johnson-Mehl-Avrami-
Kolgomorov model (see Introduction). As shown in Figure
2c,d, we can distinguish two lines having different slopes in the
Avrami plots. This means that the reaction kinetics is different
for the first and second stages of the crystal photochemical
transformation. For the first stage the Avrami exponent n is ∼1
(0.93 and 1.08 for crystals 1 and 2, respectively), which
indicates that the mechanism of the reaction is homogeneous
and also that the occurring structural transformations brought
about by the reaction do not influence further product
formation. In the second stage, n is much less than 1 (0.44 and
0.52 for crystals 1 and 2, respectively), which indicates that the
reaction proceeds with autoinhibition; that is, the further
product formation makes the reaction more difficult. It is
worth pointing out that, for both studied crystals, the values of
n are approximately the same.
The observed autoinhibition means that the more product
molecules that exist (and the fewer the reactant molecules),
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Figure 2. Relationship between the product content and UV irradiation time for (a) crystal 1 and (b) crystal 2. The Avrami plot for the Norrish-
■
●
Yang reaction in (c) crystal 1 and (d) crystal 2. ( ) First and ( ) second stages of the reaction.
the more difficult the reaction is. In connection with this
statement, we analyzed the environment of reactant molecules
after 20 min of UV irradiation (i.e., for the first stage of the
reaction) and after 160 min (i.e., for the second stage) for four
border situations:
Introduction). It should be emphasized here that, because of
the geometry of the reaction center, the formation of a five-
membered ring was not possible: the value of parameter d was
greater than 3.3 Å, and that of parameter D was greater than
3.8 Å.
As written above, at the beginning of the photochemical
crystal transformation, the geometrical parameters have values
favorable for the Norrish-Yang reaction with the participation
of 2-isopropyl. Along with the reaction progress the values of
parameters d, Δ, and ω become less favorable for 2-isopropyl
and more favorable for 6-isopropyl, which can be concluded
from Figure 3, which shows that parameter D decreases for 2-
isopropyl and 6-isopropyl and that the remaining parameter θ
is constant for both groups. It is interesting that in the first
stage of the reaction, that is, until ca. 50% conversion, the
values of the parameters do not change significantly; only in
the second stage this is the case. The changes in the values of d,
Δ, and ω explain the change in the kinetics, namely, near the
50% reaction progress stage, the geometry of the reaction
center starts to worsen for 2-isopropyl and improve for 6-
isopropyl. Nevertheless, 6-isopropyl does not participate in the
reaction (see above for the insufficient free space).
The additional reason for the observed autoinhibition
connected with intramolecular geometry is the change in the
orientation of aromatic ring C1→C6 in relation to the
carbonyl group: the value of the dihedral angle between
C1→C6 and the plane formed by atoms C1, C7, O1, and C8
gets worse from 79.1° to 86.5°.
Intermolecular interactions can also influence the auto-
inhibition of the reaction. The important contacts in this
context seem to be C−H···π interactions presented in Figure 4.
Although such contacts are obviously not as strong as typical
(1) The crystal is in the first stage of the reaction, and one
reactant molecule is only surrounded by other reactant
molecules.
(2) The crystal is in the first stage of the reaction, and one
reactant molecule is only surrounded by product
molecules.
(3) The crystal is in the second stage of the reaction, and
one reactant molecule is only surrounded by other
reactant molecules.
(4) The crystal is in the second stage of the reaction, and
one reactant molecule is only surrounded by product
molecules.
This analysis revealed that, near the reactive 2-isopropyl
group, there is a free space of a similar size and shape for all
four cases, that is, for both stages of the reaction and regardless
of the vicinity of the reactant molecule. This observation
indicates that the autoinhibition is not the result of free space
reduction with the reaction progress. The free space for the
first situation above is shown in Figure 1d.
To find the reason for the reaction autoinhibition, we
analyzed the geometry of the reaction center and state that this
geometry was one of the main reasons for the photochemical
behavior of the crystals during the first and the second stages
of the reaction. The likelihood of the Norrish-Yang reaction
can be predicted on the grounds of five intramolecular
geometrical parameters: d, D, ω, Δ, and θ (see the
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Figure 3. Change in values of the geometrical intramolecular
parameters describing the susceptibility to the Norrish-Yang reaction
■
●
for 2-isopropyl ( ) and 6-isopropyl (red ).
hydrogen bonds, they can act cooperatively.78,79 Along with
the reaction progress, the mean distance for them becomes
shorter, which can make the shift of ring C8→C13 necessary
for making the four-membered ring formation more difficult.
The next explanation of the autoinhibition of the studied
reaction was provided by the Raman spectra shown in Figure 5.
The bands characteristic for the CO stretching mode in
ketones at 1680 cm−1 and for the phenyl-carbon stretching in
aryl ketones at 1255 cm−1 decline along with the photo-
chemical reaction progress and finally disappear, which is
connected with the formation of the hydroxyl group from the
carbonyl group. These spectral features are accompanied by
the increase in the intensity of the band characteristic for the
C−O stretching vibrations in alcohols at 1030 cm−1 and the
appearance of the bands characteristic for the O−H stretching
at 3576 and 3612 cm−1. In terms of the autoinhibition it is
important that, along with the reaction progress, the characters
of the N−H···O hydrogen bond and of the carboxylate group
strongly change. It results from the determined X-ray
structures indicate that the N···O distance decreases
monotonically, which is presented in Figure 6. The observed
reduction is conjugated with the changes in the position of the
hydrogen atom in this bond. At the beginning of the reaction,
the hydrogen atom is situated at nitrogen at a distance of 1.04
Å, which indicates the salt formation. Afterward along with the
reaction progress it moves away from nitrogen toward oxygen,
and at the end of the reaction it is found almost in the middle
between both these atoms. The changes in the position of the
hydrogen atom influence the changes in the electronic
structure of the carboxylate group, which is also shown in
Figure 6.
Figure 4. Changes in the C−H···π contacts along with the Norrish-
Yang reaction progress. The progress of the reaction is presented from
red through pink to gray. Datm is the distance between the hydrogen
2
i
i
■
●
atom and the closest sp atom, C9···H29a ( ), C11···H27a ( ),
i
▲
C13···H28a ( ). The symmetry code: i = x, 1/2 − y, −1/2 + z.
Before the photochemical reaction, this group is stabilized
by a resonance effect, and the difference in CO bond lengths is
only ca. 0.02 Å (1.264 vs 1.245 Å). This delocalization
gradually decreases along with the reaction progress, and in the
final step the difference in the CO bond lengths increases to
0.06 Å (1.286 vs 1.223 Å), and the geometry of the carboxylate
group is closer to that of a carboxylic. This is accompanied by
changes in the Raman spectra: the band at 1646 cm−1
characteristic for the stretching mode of the benzoic acid
carbonyl80 appears and gradually increases along with the
reaction progress, and the strong symmetric carboxylate anion
stretching at 1387 cm−1 decreases, both evidencing that the
electron charge in the carboxylate becomes less delocalized.
This carboxylic-like structure is revealed in the Raman
spectra after ca. 50% reaction progress, that is, at the stage
when reaction kinetics changes, which suggests that the change
in the reaction kinetics can be associated with the alterations in
the character of the carboxylate group (electron donating)
toward the carboxylic group (electron withdrawing). It is
worth adding that the electron effects of the above-described
type can be indicated as the next explanation of the
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Figure 5. Raman spectra for crystal 1.
observation made in the past that 4-(2,4,6-triisopropyl-
benzoyl)benzoic acid undergoes the Norrish-Yang reaction in
crystals with difficulty.20
The structural transformations induced by the Norrish-Yang
reaction also include modifications in the values of the unit cell
parameters: parameter a decreases, and b increases, both in a
monotonic manner; c remains almost constant, and the angle β
becomes more obtuse along with the reaction progress, which
is presented in Figure 7. The values of the cell parameters also
change with the progress of the reaction conducted at 0.2 GPa.
The character of these changes is the same as at ambient
pressure: after 10 min of UV irradiation of the crystal, a
decreases from 26.50(2) to 26.34(8) Å, b increases from
8.5258(8) to 8.601(3) Å, c almost does not alter (11.7775(11)
vs 11.767(3) Å), and β increases from 92.72(2)° to 93.23(8)°.
All these photoinduced modifications indicate that the
Norrish-Yang reaction of the studied compound also proceeds
at 0.2 GPa.
To gain knowledge about the influence of high pressure on
the kinetics of the Norrish-Yang reaction of the studied
compound, at first we analyzed the influence of high pressure
on intra- and intermolecular geometry. It can be said that there
are no changes in the intramolecular geometry with the
increase of pressure, even in the geometry of the reaction
center. Moreover, the high pressure of 0.2 GPa does not have a
significant impact on intermolecular interactions in which the
atoms of the reaction center take part. In accordance with this,
the free space existing near the reactive 2-isopropyl group in
ambient conditions is also observed at high pressure (see
Figure 6. Changes in the geometry of (a, b) the N···H···O hydrogen
bond and (c) the carboxylate group along with the reaction progress.
Figure 1e), and its volume is 16.0(4) and 14.0(3) Å3,
respectively. On the one hand, the above findings indicate
that the kinetics of the Norrish-Yang reaction of the studied
compound should be similar at ambient pressure and 0.2 GPa.
On the other hand, it should be taken into account that, in
ambient conditions, the studied photochemical reaction
proceeds with the increase of the unit cell volume (see Figure
7) and that high pressure by counteracting this increase should
decrease the reaction rate. The decrease of the rate of the
Norrish-Yang reaction at high pressure was also observed in
the case of another compound.81
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Figure 7. Changes in the values of the cell parameters at ambient pressure.
CONCLUSIONS
AUTHOR INFORMATION
Corresponding Authors
■
■
The X-ray diffraction and Raman spectroscopy studies were
undertaken in order to describe the kinetics of the Norrish-
Yang reaction of 1,3,5,7-tetraazatricyclo[3.3.1.13,7]decane 4-
(2,4,6-triisopropylbenzoyl)benzoate in crystals. The Norrish-
Yang reaction proceeds with the participation of the 2-
isopropyl group. The overall shape and size of reactant and
product molecules is very similar: only the reacting fragments
and one aromatic ring shift significantly as a result of the
reaction. The studies revealed that the reaction kinetics
changes at ca. 50% conversion. The two stages of the reaction
were described by the JMAK model. In the first stage the
reaction proceeds homogeneously with a constant rate, but in
the second stage it proceeds with autoinhibition. The observed
autoinhibition is a result of the changes in the molecular
geometry, in the crystal lattice structure, and in the electron
properties of substituents. The Norrish-Yang reaction also
proceeds in crystals at 0.2 GPa, which was stated on the
grounds of the characteristic changes in the unit cell
parameters along with the reaction progress. The reaction
should proceed slightly slower at 0.2 GPa, because high
pressure counteracts the unit cell increase, which is demanded
for the reaction to proceed. The pressure of 0.2 GPa does not
have influence on the intramolecular geometry and the volume
of the free space near the reaction center.
Krzysztof A. Konieczny − Advanced Materials Engineering and
Modelling Group, Wrocław University of Science and
Technology, 50-370 Wrocław, Poland; orcid.org/0000-
0003-4618-5154; Email: krzysztof.konieczny@pwr.edu.pl
Ilona Turowska-Tyrk − Advanced Materials Engineering and
Modelling Group, Wrocław University of Science and
Technology, 50-370 Wrocław, Poland; orcid.org/0000-
0001-8534-1944; Email: ilona.turowska-tyrk@pwr.edu.pl
Authors
Anna Szczurek − Department of Mechanics, Materials Science
and Engineering, Wrocław University of Science and Technology,
50-370 Wrocław, Poland; orcid.org/0000-0003-3977-
9691
Julia Bąkowicz − Advanced Materials Engineering and
Modelling Group, Wrocław University of Science and
Technology, 50-370 Wrocław, Poland
Renata Siedlecka − Department of Organic Chemistry, Wrocław
University of Science and Technology, 50-370 Wrocław, Poland
Arkadiusz Ciesielski − Section of Theoretical Chemistry and
Crystallography, University of Warsaw, 02-093 Warsaw,
Pasteura 1, Poland
́
Michał K. Cyranski − Section of Theoretical Chemistry and
ASSOCIATED CONTENT
Crystallography, University of Warsaw, 02-093 Warsaw,
Pasteura 1, Poland
■
Accession Codes
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.cgd.0c00245
CCDC 1978380−1978398 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
Notes
The authors declare no competing financial interest.
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(17) Koshima, H.; Fukano, M.; Ojima, N.; Johmoto, K.; Uekusa, H.;
Shiro, M. Absolute Asymmetric Photocyclization of Triisopropylben-
zophenone Derivatives in Crystals and Their Morphological Changes.
J. Org. Chem. 2014, 79, 3088.
ACKNOWLEDGMENTS
■
This work was financed by the statutory activity subsidy of the
Polish Ministry of Science and Higher Education.
(18) Bąkowicz, J.; Olejarz, J.; Turowska-Tyrk, I. Steering Photo-
chemical Reactivity of 2,4,6-Triisopropylbenzophenonate Anion in a
Crystalline State. J. Photochem. Photobiol., A 2014, 273, 34−42.
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