Methoxy group, twisting

In 1,8-bis(dimethylamino)naphthalene steric and lone pair interactions are minimised in a structure (Einspahr et al., 1973) having the amino groups twisted and displaced above and below the plane of the naphthalene ring, as in [53] in which the almost planar naphthalene ring is shown as a dashed line. In l,8-bis(dimethylamino)-2,7-dimethoxynaphthalene, steric interactions involving the methoxy substituents bring about a further distortion as in [54] (Woolf, 1980). 

Ni(II) complex (Fig. 18) reveals that the metalloclip has a twisted structure. Two of the methoxy groups are pointing into the cavity, in this way blocking the access of a guest molecule. As a consequence, resorcinol is not bound in the cleft of 31a. 

The same authors have also studied compounds 86 and 87 having a methoxy group (Fig. 15). These compounds could exist either in the chair form with an axial (88) or an equatorial methoxy group (89), or in the twist-boat 90. Conformer 88 is disfavored sterically but is favored electronically, whereas the twist boat 90 with a syn clinal methoxy group is favored electronically and does not suffer from severe steric hindrance. It was found... 

Theoretical and experimental studies revealed a mechanistic twist of the concerted [8+2] cycloaddition between dienylbenzo[c]furans and dimethyl acetylenedicarboxylate (DMAD). Thus, DFT calculation at the (U)-B3LYP/6-31+G(d) level had suggested a stepwise mechanism involving the formation of a zwitterionic intermediate for the [8+2] cycloaddition between DMAD and dienylbenzo[c]furans with electron-donating methoxy groups in the diene moiety. When no electron-donating substituents are present in the diene moiety of the dienylbenzo[c]furan, computational results indicated an alternative mechanism in which a [4+2] reaction occurs between the furan moiety and DMAD, and was followed by a [l,5]-vinyl shift <07JA10773>. 

The stabilization of benzhydryl 31 and triphenylmethyl 2 is less than additive, as expected for the non-planar propeller-like structures of these radicals, which do not allow the development of full conjugation. The angle of twist is probably very similar in benzhydryl and trityl radicals 73) and one is tempted to attribute to each twisted phenyl an additive stabilization of 6 kcal mol"1. On the other hand two cyano groups in 32 likewise stabilize a radical less than additively. Phenyl and cyano (33) and phenyl and methoxy (34) show additive stabilization. For one cyclopropyl group in 35 a little more than 1 kcal mol-1 stabilization can be counted and additivity follows consequently for 36. The captodative radical 37 is stabilized according to additivity... 

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