Amides nonbonded interactions

Potential functions induced-dipole terms, 84-85 minimization, 113-116 nonbonded interactions, 84-85 Potential of mean force, 43, 144 Potential surfaces, 1,6-11, 85, 87-88, 85 for amide hydrolysis, 176-181,178,179, 217-220, 218... 

Fig. 7.13 Characteristic nonbonded interactions in N-acetyl N -methyl serine amide. Torsional angles to construct this figure were taken from K. Siam, S. Q. Kulp, J. D. Ewbank, and L. Schafer, J. Mol. Struct, 184 (1989) 143.

Nonbonded interactions have generally not been included in our force field, except where an unusually close contact is present, such as H - H in (Gly) I (Moore and Krimm, 1976a). The main reason is that they ordinarily have a small influence on the medium-range frequencies, and in particular no effect on amide I or amide II splittings (V. Naik and... 

The essence of the CFF method as applied to nonbonded interactions in carboxylic acids and amides, may be illustrated by Table 1 and Figs. 2-3 from the bench-mark" paper by Hagler, Lifson and Dauber (1979). The table represents the root mean square deviation (rms dev) between calculated and measured observables for three force fields CFF "12-6-1" (i.e. "12-6" for LJ and "1" for Coulomb). 

Amides Primary Secondary 3540-3500 (w) 3400-3380 (w) 1310-1250 (s) 1150-1095(m) 3491-3404 (m-s) 1190-1130 (m) 931-865 (m-s) 430-395 (w-m) Both bands lowered ca 150 cnr1 in solid state and H bonding Interaction of NH bending and CN stretching lowered 50 cnr1 in nonbonded state Rocking of NH2 Two bands lowered in frequency on H bonding and in solid state... 

Figure 3.9a may also represent the interaction of a nonbonded ( lone-pair ) orbital with an adjacent polar n or a bond [67]. If a polar n bond, one can explain stabilization of a carbanionic center by an electron-withdrawing substituent (C=0), or the special properties of the amide group. If a polar a bond, we have the origin of the anomeric effect. The interaction is accompanied by charge transfer from to A, an increase in the ionization potential, and a decreased Lewis basicity and acidity. These consequences of the two-electron, two-orbital interaction are discussed in greater detail in subsequent chapters. 

During the above study, it became apparent that stannyl amides exhibit lower oxidation potential compared with the original nonstan-nylated amides. These phenomena have also been reported by Yoshida et al. in their measurements of oxidation potentials of a-stannyl derivatives (Table 7). Yoshida and co-workers explained that the decrease in the oxidation potential is attributed to the rise of the HOMO level of the stannyl (or silyl) compound by interaction of the carbon-tin (or carbon-silicon) a bond and the nonbonding p orbital of the oxygen atom. 

Bauld, N. L. Cessac, J. Holloway, R. L. l,3(Nonbonded) carbon/carbon interactions. The common cause of ring strain, puckering, and inward methylene rocking in cyclobutane and of vertical nonclassical stabilization, p)U amidalization, puckering, and outward methylene rocking in the cyclobutyl cation, J. Am. Chem. Soc. 1977,99, 8140-8144. 

Treatment of the laterally lithiated amide generated from lactam 273 with LDA with /ra r-2-phenylsulfonyl-3-phenyloxaziridine 33 afforded hydroxyl product 274 in 85% yield as a single isomer <1999JOC8627>. Use of (+)-(camphorsulfonyl)oxaziridine 202 gave similar results. The /ra t-stereoselectivity is consistent with the earlier finding that the hydroxylation stereochemistry is controlled by nonbonded steric interactions in the transition state such that the oxygen of the oxaziridine is delivered from the sterically least hindered direction. Treatment of 275 with LDA followed by (+)-(camphorsulfonyl)oxaziridine 202 afforded hydroxyl product 276 in 47% yield and 60% ee <1997T8881>. 

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