Methyl tilt

The donor-acceptor picture readily accounts for the observed methyl tilting and distortion.96 Figure 3.67 illustrates the asymmetric bending of each C—H bond of... 

Figure 3.67 Methyl tilt in CH3NH2, showing individual N-C-H angle deviations (solid lines) from the mean value (111.3 0.1°) and the overall tilt angle (dotted line) of the methyl symmetry axis with respect to the C—N bond vector. The anti C—H bond (circles) corresponds to Fig. 3.59(a) at (p = 0°.

CH3NH2, showing the 6° variation in N-C-H angle as the H rotates from gauche to anti alignment with the vicinal nN lone pair. The overall methyl tilt (dotted line) is evidently dominated by the strong outward tilting of the C—H bond anti to the lone pair, as discussed above (cf. Fig. 3.66 and Table 3.24). 

The general role of aCH orbitals and hyperconjugative interactions in methyl tilting was suggested much earlier on qualitative grounds H. P. Hamlow, S. Okuda, and N. Nakagawa, Tetrahedron Lett. 1964 (1964), 2553 and note 141. 

Fig. 22a. Geometries and energetics for the reactions PdH2 - Pd - - H2, PdH(CH3) - Pd 4- CH4, and Pd(CH3>2 - Pd -I- C2H. The angle between the Pd—C bond and the vector from the C atom to the center of mass of the methyl hydrogen atoms is defined to be the methyl tilt [67] b GVB orbital for the Pd—C bonds at the transition state for the reaction Pd(CH3)2 - Pd -I- C2H and the GVB orbitals for the PdH bond for the reaction PdH2 - Pd -I- H2. The Mulliken populations are listed with each orbital to show the hybridization of each orbital [67]...

A local C3V symmetiy for the CH3 group and linearity for the N3 gionp are assnmed. There is essentially no methyl tilt angle. The nozzle temperature was 333 K. 

Assumed. ) Methyl tilt angle, toward outside. ... 

Using this strategy, constmction of multilayer films of - O. fim thickness by self-assembly of methyl 23-ttichlorosilyltticosanoate (MTST) on siUcon substrates has been demonstrated (Fig. 9) (165). The linear relationship between the film thickness and the layer number showed a slope of 3.5 nm /layer. Filipsometry data, absorbance intensities, and dichroic ratios for the multilayers all suggest that the samples were composed of distinct monolayers. However, ir data indicated that there maybe more tilting or disordering of the alkyl chains in the seven-layer sample than for the monolayer samples. 

Zareba et al. [165] described the crystal structure of the chiral 4-(l-methyl-heptyloxycarbonyl)-phenyl 4-heptyloxytolane-4 -carboxylate (C7-tolane) which shows monotropic antiferroelectric and ferroelectric phases. The single-crystal X-ray analysis of this compound shows that the crystal has a smectic-like layer structure composed of largely bent molecules where the chain of the chiral group is almost perpendicular (86°) to the core moiety. Within the layers, the molecules are tilted. The central tolane group of the molecule is roughly planar. 

Fig. 10 Estimation of the tilt angle for an alkane between gold electrodes, determined by fitting the computed IETS spectrum with the experiment (panel b below). Result is a 40 degree tilt angle perpendicular to the plane of the carbon chain, as illustrated in the lighter shade structure in the sketch (b) above. Sketch (a) above and panel (a) below refer to the alkane tilted in the plane of the carbon chain. The structures in sketch (a) do not fit so well an those in (b), suggesting the methyl group position shown in (b) above. From [107], Reproduced by permission of the PCCP Owner Societies...

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