Structural studies on nitrosobenzene and 2-nitrosobenzoic acid. Crystal and molecular structures of cis-azobenzene dioxide and trans-2,2'-dicarboxyazobenzene dioxide

Abstract

both in solution and in the crystalline state, provide a fruitful area for a combined crystallographic and chemical study.7 Aromatic C-nitroso compounds can exist as blue or green colored monomers(1) or colorless dimers (2). In the dimeric state, cis (2a) and trans (2b) isomers are possible. As a general rule, but one with (5) C.

The structure of a benzoquinone diimine N,N'-dioxide derivative

“…The bond angles at N(1) (see Table 2) indicate an sp 2 hybridization, thus suggesting the presence of an extensive zr conjugation. In fact, the average N---O distance, 1.279 (3)A, is quite similar to that found in azo dioxide derivatives, or nitroso dimers [see, e.g., cis-azobenzene dioxide (Dieterich, Paul & Curtin, 1974), with an average of 1.264(4)A or trans-2,2"-dicarboxyazobenzene dioxide (Dieterich et al, 1974) with 1.267 (3)/~], or in p-azoxy anisole [1.279 (4) A (Krigbaum, Chatani & Barber, 1970)]. It is also equal to those found in p-methoxyindophenol N-oxide, 1.266 (4)A (Romers & Hesper, 1966) and in paramagnetic nitroxides: for example, 2,2,5,5-tetramethyl-3-X-l-pyrrolidinyloxy derivatives have an N--O separation of 1.272 (3)A for X = COOH (Ament, Wetherington, Moncrief, Flohr, Mochizuki & Kaiser, 1973;Wetherington, Ament & Moncrief, 1974) and 1.272(5)A for X=NOH (Chion & Thomas, 1975).…”

2-Carboxy- and 2,7-Dicarboxy-4,5-benzotropone: Hydrogen-Bonding Patterns of a β-Keto Acid and a Related β-Keto 1,5-Diacid

“…This shortening relative to (I) presumably reflects lessened C==O polarization associated with the loss of resonance-enabling planarity in (II) relative to (I). Although averaging of carboxyl C---O bond lengths and C---C---O angles by disorder occurs in some dimeric acids (Dieterich, Paul & Curtin, 1974;Borthwick, 1980), it is not significant here. rack ribbon.…”

2,4,6-Trichlorobenzoic Acid: Structure and Hydrogen-Bonding Pattern

“…Disordering in the carboxyl group is displayed by the C--O bond length and C--C--O angles. This disordering is common in dimeric acids (Dieterich, Paul & Curtin, 1974). The C--O bond lengths found in the title compound are 1.234 (6) and 1.269 (6),~ in molecule A, 1.233 (6) and 1.250 (6),~ in molecule B, and 1.241 (6) and 1.244 (6),~, in molecule C. The C----C-O angles found are 116.7(4) and 118.2(4) ° in molecule A, 117.3(4) and 117.8(4) ° in molecule B, and 117.8 (4) ° for both of the angles in molecule C. These can be compared with typical lengths of 1.21 (3),~, for the C==O and 1.31 (2)A for the C--O(H) bond distances, and angles of 112 (2) ° for C---C--O(H) and 123 (2) ° for C---C=O in some of the more highly ordered carboxyl dimers (Borthwick, 1980).…”