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Methyl group orienting effect

Additional support for this hypothesis was provided by the observation of an inverse "odd-even" or parity effect for the wettabilities of polar contacting liquids on the CF3-terminated films (see Figure 5). The parity effect has been observed in CH3-terminated monolayer films and arises from the dependence of the orientation of the terminal methyl groups upon the total number of carbon atoms in the adsorbates (i.e., the chain length) [39,40]. Films comprised of adsorbates with odd chain lengths (odd-numbered SAMs) have terminal methyl groups oriented more parallel with respect to the surface of gold than films comprised of adsorbates with even chain... [Pg.64]

For CH3—CH3 or CH3—CHO, there are three equivalent configurations for a complete rotation of the methyl group about the C—C bond. The potential function possesses three potential energy minima and maxima as illustrated in Fig. 19. Since the methyl group is symmetric, the moments of inertia of the molecule do not depend on the orientation of the methyl group. The effects of internal rotation are transmitted to the rotational spectrum somewhat indirectly. [Pg.314]

FIGURE 16.15 Orientation effects in intramolecular reactions can be dramatic. Steric crowding by methyl groups provides a rate acceleration of 2.5 X 10 for the lower reaction compared to the upper reaction. (Adaptedfrom Milstien,. S., and Cohen, L. A., 1972. Stereopopnlation control I. Rate enhancements in the laetonization of o-hyelroxyhyeJroeinnamie acid. Journal of the American Chemical Society 94 9158-9165.)... [Pg.513]

Nonadditivities of individual effects of vicinal substituents were recognized early. Dalling and Grant (100,101) reported that upheld (i.e., negative) a-ICSs of 2.5 to 3.5 occur at signals of substituted carbon atoms in 1,2-dimethylcyclohexanes if the methyl groups are in gauche orientation to each... [Pg.276]

Much work has been done to determine sets of substituent effects in specific conformationally mobile or rigid frameworks, since a knowledge of such effects often furnishes valuable conformational information. For instance, it was concluded from yg- and 8-SCS values that substituents (X = OH, I) on the C(19) methyl group in some cholest-S-enes prefer an antiperiplanar orientation [X-C(19)H2-C(10)-C(1)] with respect to C(l) (81). In the following, SCS information for various classes of cyclic systems is discussed, with particular emphasis on configurational and conformational analysis. [Pg.302]

Additional experiments were performed to examine the role of the molecular size of the host enantioselectivity. Since the methyl groups in methylated jS-CD orient themselves toward the center of the cavity, it is expected that decreasing the extent of methyl derivatization in jS-CD from 21 (the permethylated jS-CD) to 14 methyl groups increases the effective size of the cavity." " As a matter of fact, the enantioselectivity of valine (kolkL = 0.32 with 21-methyl j8-CD) increases to W l = 0.18 with 14-methyl jS-CD. No significant effect of the cavity size is observed with the smaller alanine. [Pg.221]


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See also in sourсe #XX -- [ Pg.343 ]

See also in sourсe #XX -- [ Pg.581 ]




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Methyl effect

Methyl group

Orientation effect

Orienting effect

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