The crystal structures of tetramethylene glycol dibenzoate (1). tetramethylene glycol di-para-chlorobenzoate (2), and tetramethylene glycol di-para-nitrobenzoate (3) have been solved by direct methods in order to establish the possible conformations of the methylenic sequence in poly(tetramethy1ene t$rephthalate), poly(4GT). Compound 1 has a triclinic unit cell of dimensions a = 7.870(3), b = 8.574(3), c = 12.993(4) A; a = 83.76(3), p = 89.92(3), y = 64.68(3)"; Z = 2, space group P I . For 2 the unit cell is also triclinic and has dimensigns a = 5.916(3), b = 7.599(2), c = 10.404(2) A; a = 67.81(2), p = 77.47(2), 7 = 81.63(3)'; Z = 1, space group P1. The unit cell dimensions of 3 are a = 6.086(1), b = 1 I .475(3), c = 13.162(3) A and p = 101.93(2)", Z = 2. The space group is P 2 , l c . The structures were solved by direct methods using 2682, 969, and 781 observed reflections for 1, 2, and 3, respectively. The refinements were concluded when R reached the values of 0.042, 0.046, and 0.045, respectively. The conformation of the methylenic sequence varies depending on the substituent on the benzoate group. The conformation observed in 1 is t g -t t t , it is t t t t t for 2, and t g -t g t for 3 (t = trans, g = gauche). Although the equivalent fiber repeat of 3 coincides with the observed fiber repeat for a-poly(4GT), this does not imply that 3 and a-poly(4GT) have the same conformation. Compound 2 allows for the modelling of the p-form of poly(4GT). However, this does not lead to a clear choice between the two structures reported for this form. The two distinct conformations proposed for the p-form of poly(4GT) are distinguished on the basis of their ir and Raman spectra. The comparison of the spectra of the model compounds reveals that, in ir, for an all-trans conformation there is no absorption band at 1383 cm-' but one is present at 1395 cm-I. This situation that is observed in the ir spectra of p-poly(4GT) led us to propose that this form has the all-trans conformation as proposed by Hall and Pass. This choice is further supported by the presence of three bands at 1047, 1347, and 1405 c m ' in the Raman spectra of p-poly(4GT). These three bands are only observed in the model compounds having the all-trans conformation.ALLAN PALMER, SUZIE POULIN-DANDURAND et F R A N~O I S BRISSE. Can. J. Chem. 63, 3079 (1985). Les structures cristallines des bis(benzoate) (I), bisbara-chlorobenzoate) (2) et bis@ara-nitrobenzoate (3) du tetram6thylene glycol ont ttC rCsolues dans le but d'etablir les conformations possibles des sequences mjthyltniques du poly-(terephtalate de tetramkthylene), poly(4TG). Le composC 1 appartient au groupe d'espace triclinique P 1, avec a benzoate. On a observe les conformations suivantes: t g -t t r pour le compose 1, t t r i t pour le composC 2 et t g -t g t pour le compose 3 (t = trans, g = gauche). Le fait que la pCriode de fibre Cquivalente du composC 3 coincide avec la pCriode de fibre observie pour I'a-poly(4TG), n'implique pas necessairement que ces deux composCs ont la mCme conformation. ...