Structural studies of benzene derivatives. VII. Refinement of the crystal structure of p-dinitrobenzene

Abstract

C6H4N204 is monoclinic, space group P21/n , with a = 11.137(2), b = 5.461 (1), c = 5.684(3) /l,, fl = 92.22 (4) ° , Z = 2. The final R is 0.0408 for 559 independent counter intensities. The benzene ring has mmm symmetry within experimental error. The distortions from 6/mmm symmetry are quite marked, and involve bond lengths as well as angles; they testify to the strong a-electron-withdrawing character of the substituent. The value of the internal angle at the ipso atom, CtNo 2 = 123.4 (1) °, is in good agreement with values reported for other molecules where the nitro group is para to a 7r acceptor.

Structural studies of benzene derivatives. X. Refinement of the structure of p-chlorobenzoic acid

“…* As in previous cases (Di Rienzo, Domenicano & Riva di Sanseverino, 1980, and references therein), other weighting schemes gave higher dispersions for the mean values of the minimized function over ranges of either I Fol or sin 0/L and afforded a less symmetrical C hexagon. Calculations were carried out on the Univac 1100/ 22 computer of the University of Rome and on the HP 21MX minicomputer of the CNR Research Area.…”

“…Thus the published 'substitution' structure of chlorobenzene should be considered as rather inaccurate, as far as the ipso region of the ring is concerned, and a revised structure has recently been proposed (Schultz, Hargittai & Domenicano, 1980). A similar problem is posed by the microwave structure of nitrobenzene (H~g, 1971), which appears to be unrealistically distorted in the ipso region (Di Rienzo, Domenicano & Riva di Sanseverino, 1980).…”

Structure of 1,2-dinitrobenzene

“…Although the crystal structures of 1,4-and 1,3-dinitrobenzene have been known for many years [para isomer : James, King & Horrocks (1935), Di Rienzo, Domenicano & Riva di Sanseverino (1980); meta isomer: Archer (1946), Colapietro, Di Rienzo, Domenicano, Portalone & Riva di Sanseverino (1977)], only cell dimensions have been reported for the ortho isomer [Hertel & Schneider (1930), in reasonable agreement with our values; also by Chaudhury & Talapatra (1955), in poor agreement with our values]. One of us tried unsuccessfully to determine the structure in his first attempt at crystal structure analysis (Herbstein, 1948) and then returned to it recently when searching for a suitable demonstration structure for a course project.…”

Structure of 1-(4-nitrophenyl)pyrrole, -imidazole, -pyrazole and -1,2,4-triazole derivatives

“…The internal C--C---C angle of the benzene ring to which NO2 is bonded ranges from 121.1 (4) to 124.8 (9) °. For the series, the tr-electronwithdrawing character of the NO2 group (Di Rienzo, Domenicano & Di Sanseverino, 1980) is suggested.…”