S. Kudoh et al. / Journal of Molecular Structure 524 (2000) 251–258
253
dimethylaminomethanol,
(CH3)2NCH2OH,
has
gauche and trans conformations around the
(CH3)2N–CH2OH and (CH3)2NCH2–OH bonds, nine
conformers, TT, TGϩ, TGϪ, GϩT, GϩGϩ, GϩGϪ,
GϪT, GϪGϩ and GϪGϪ are possible. The notation
of conformers follows the rules proposed by Hamada
et al. [23], where plus and minus superscripts refer to
opposite angles around the rotational axes. The former
letter represents the relative position of the oxygen
atom and the lone pair of the nitrogen atom, while
the latter represents that of the nitrogen atom and
the hydrogen atom of the OH group. Among the
possible conformers, TGϪ, GϪT, GϪGϪ, and GϪGϩ
are equivalent to TGϩ, GϩT, GϩGϩ, and GϩGϪ,
respectively. The GϩT and GϩGϩ conformers seem
to be unstable because of the repulsion between the
lone pairs of the nitrogen and oxygen atoms. As a
result, three nonequivalent conformers, TT, TG
(TGϩ and TGϪ) and GG (GϩGϪ and GϪGϩ) are
deemed stable. The optimized geometry of TT, TG
and GG obtained by the DFT calculations is shown
in Fig. 3. The calculated values of the structural
parameters are given in Table 2. The C4–N and
Fig. 2. A difference infrared spectrum of (CD3)3N and NO2 obtained
upon irradiation at all lines of Arϩ laser (100 mW cmϪ2) for 30 min
subsequent to 580 nm irradiation for 4 h. The decreasing bands due
to the reactants are indicated by “O”. The absorption changes of
NOx and impurity are indicated by “X”.
the intensities of the new bands decreased and some
bands of the final products were observed, as shown in
Fig. 2. The 1872 cmϪ1 band was easily assigned to
NO by comparison with the reported spectra for the
normal and 18O isotope species [18]. Other bands
showed large isotope shifts caused by deuteration.
Two bands for the final product were observed at
2693 and 2670 cmϪ1 in the O–D stretching region,
although the corresponding bands for the normal
and 18O species could not be identified because of
overlapping with the bands due to impurity water.
Therefore, we tentatively assigned the observed
bands for the final product to dimethylamino-
methanol. The observed wavenumbers and relative
intensities are summarized in Table 1 with those for
the normal and 18O isotope species reported
previously [18].
˚
O–C4 bonds of GG are about 0.02 A longer and
˚
0.03 A shorter than those of TG or TT, respectively.
The C4–N–C1 and H–O–C4 bond angles of GG are 2Њ
smaller than those of TG or TT. These findings imply
that the GG conformer is stabilized by hydrogen-bond
interaction between the lone pair of the nitrogen and
the hydrogen of the OH group. Our calculation has led
to the conclusion that GG is the most stable, although
the energy of TG is higher than GG by only
0.77 kJ molϪ1, while TT is the least stable among
the three and the energy is higher than GG by
3.89 kJ molϪ1. Fernandes et al. [24] performed an
MM2 calculation and obtained the relative energies
of GG, TG and TT to be 0.0, Ϫ13.9, and
19.8 kJ molϪ1, respectively. The stabilities for the
conformers totally disagree with ours. They also
performed ab initio calculations using a basis set of
6-31Gء
. The relative energies for GG, TG, and TT
3.2. DFT calculations
were calculated to be 0.0, 0.75 and 4.01 kJ molϪ1
respectively, which are consistent with our results.
,
In order to confirm our assignments, we performed
DFT calculations using the Gaussian 94 program
[20] with the 6-31ϩϩGءء
basis set, where the hybrid
density functional [21], in combination with the Lee,
Yang and Parr correlation functional (B3LYP) [22],
was used to optimize the geometrical structures. Since
The calculated wavenumbers and relative inten-
sities for the most stable conformers, GG and TG,
are compared with the observed values in Table 1.
The strongest bands due to the C–O stretching
mode for GG were predicted to be 1077, 1056, and