Influence of surface area on efficiency of DSSC
Russ.Chem.Bull., Int.Ed., Vol. 66, No. 1, January, 2017
73
frequencies of the calculated adducts were real. In both
cases, a hydrogen bond formed, this bond in molecule A
being stronger than that in B (see Fig. 3). In azomethine A,
the torsion angle containing the reduced bond >C=N—
which have positive chemical shifts, while the chemical
shifts of the signals of methylene groups are negative. The
1
13
geꢀ2D H— C HSQC experiments can be used to record
1
13
crossꢀpeaks of the signals from groups of H and C atoms
linked by one chemical bond.
(
ϕ(C(6)—C(5)—N(1)—C(8))) changed and became equal
to 46.3°. The planarity of molecule B was distorted. The
torsion angle ϕ(C(3)—C(10)—H(5)—N(1)) was 10.5°.
A change in the geometric structure and the formation of
a hydrogen bond were reflected in the values of the total
electron energy and the Gibbs free energy. The A + EtOH
adduct proved to be energetically more favorable comꢀ
pared to the B + EtOH adduct: ΔЕ((A + EtOH) –
Figure 4 presents a fragment of the NMR spectrum of
azomethine before the hydrogenation. This spectrum
shows a heteronuclear crossꢀcorrelation signal at δC 149
and δH 5.45, which is indicative of a chemical bond beꢀ
tween the nuclei of the —N=CH— group. The same
approach was used to confirm the hypothesis of the existꢀ
ence of enamine in tautomeric equilibrium with azoꢀ
methine. The concentration of enamine in the solution
was much lower, and the characteristic peaks of the
–
1
–
–
(B + EtOH)) = 2.73 kcal mol , ΔG°298((A + EtOH) –
(B + EtOH)) = 1.53 kcal mol . The results of calculaꢀ
–
1
tions suggest that in a protic solvent, azomethine moleꢀ
cules easily form hydrogen bonds with solvent molecules,
thus influencing the imineꢀenamine tautomeric equilibriꢀ
um and the type of the bond reduced in the course of the
liquidꢀphase hydrogenation amination.
Data on the electron density and charge distribution in
the molecules were obtained in terms of the NBO theory.
In molecule A , the charge on the nitrogen atom of the
—NH—CH= group at δ 135 were not manifested (JMOD
C
13
C NMR). The characteristic heteronuclear crossꢀcorreꢀ
lation signal at δ 135 and δ 7.53 was recorded by geꢀ2D
C
H
1
13
H— C HSQC, which is an order of magnitude more
sensitive technique (Fig. 5). This signal ultimately conꢀ
firms the chemical structure of enamine. Therefore, it was
demonstrated that in ethanol the tautomeric equilibrium
of the condensation product of propanal with 4ꢀaminoꢀ
benzoic acid is shifted toward the imine form, which is in
>
C=N— bond is –0.459 e (fractional elementary charge);
1
5
on the carbon atom, 0.192 e. In molecule B, the charge on
atom 2 of the >C=C< bond (see Scheme 2) is –0.022 e; on
atom 3, –0.227 e. The following values were determined
for the adducts. In the A + EtOH adduct, the charge on
the nitrogen atom is –0.493 e; on the carbon atom, 0.212 e.
In the B + EtOH adduct, the charge on atom 2 of the
agreement with the data published in the literature. Howꢀ
ever, as mentioned above, the imineꢀenamine equilibrium
depends on many factors. The data on different ratios
1
6,17
of these forms were reported previously.
The hydroꢀ
genation produced a new compound, which is structurally
similar to the starting compound and which contains
>
–
C=C< bond (see Scheme 2) is –0.029 e; on atom 3,
0.218 e. The interaction of a hydrogen molecule with
a —CH —NH— group instead of —N=CH— and
2
—NH—CH= groups. This is confirmed by the analysis of
1
13
a noble metal surface can give rise to different forms of
hydrogen, such as atomic hydrogen, hydrogen dissolved
in a metal crystal lattice, a partially positively charged
form of hydrogen, a partially negatively charged form of
the geꢀ2D H— C HSQC spectrum (Fig. 6). It can be
seen that the signal of the carbon atom of the adduct of
molecule A with a characteristic chemical shift (δC 51)
correlates with the signal of hydrogen atoms (δH 3.22).
9
hydrogen, and adsorbed molecular hydrogen. Taking into
This crossꢀpeak is characteristic of the CH group. Hence,
2
account the fact that hydrogen on the palladium surface
bears a partial positive charge, it can be suggested that the
reduction of >C=N— and >C=C< bonds starts with
the structure of 4ꢀ(Nꢀpropyl)aminobenzoic acid was unꢀ
ambiguously confirmed.
the interaction of the atomic p orbital of nitrogen or of
δC
z
the π system of >C=C< atoms of molecules A and B with
activated hydrogen depending on the type of the unsaturꢀ
ated bond.
In order to establish the structures of the reduced comꢀ
pound and the reaction product and to clearly describe the
hydrogenation, we used modern 1D and 2D NMR spectroꢀ
scopy techniques. This approach is the major and often
1
1
1
1
44
46
48
50
the only method of investigation of the structures of small
152
organic molecules.1
0—14
In the present study, we employed
1
1
54
56
CH
the combined analysis of the results of 1D Jꢀmodulated
13
spinꢀecho (JMOD) C NMR spectroscopy and geꢀ2D
1
13
heteronuclear H— C HSQC experiments. The JMOD
13
13
C NMR and C APT NMR experiments, as well as the
5.6
5.5
5.4
1
5.3
5.2
δH
improved 1 C DEPT technique, allow the identification
3
13
Fig. 4. Fragment of the geꢀ2D H— C HSQC NMR spectrum
of the signals of methyl groups and atoms of CH groups,
of azomethine in ethanol.
Kalmykov
