large excess of ethanol at 75°C. k ( l a ) = 1.54 x lo-*, k (1 b) = 1.06 x k ( I c ) = 4 . 7 7 ~1 0 -~, k ( l d ) = 1 . 8 3 ~1 0 -~.
[6] The longest wavelength absorption band ofthiazolidine-2-thione appears at 280 nm, and the absorption coefficient is 13200. [71 Crystal data for 1 a at 296K: C,H,,NOS,, M = 203.32, monoclinic, space group C2ic, a = 33.524(3), b = 6.258(2), c = 10.459(3) A, 0 = 106.71(1)", V = 2101.5(9) A'. 2 = 4. pealed = 0.642 g ~m -~.
Anisotropic refinement of all non-hydrogen atoms using 1271 reflections with 1 > 30(1), from 1725 unique data collected, gave R = 0.048 and Rw = 0.064. Crystal data for I d at 296K: C,H,NOS,, M =161.24, monoclinic, space group P2,/n. u = 7.3517(8). b =13.9516(6), c =7.3806(6) A, 0 =104.320( 7)", Y = 733.5(1) A', Z = 4, psaird =1.406 gcm-'. Anisotropic refinement of all non-hydrogen atoms using 996 reflections with I > 3u([), from 1154 unique data collected. gave R = 0.083 and Rw = 0.119. Further details of the crystal structure investigation are available on request from the Director of the Cambridge Crystallographic Data Centre, 12 Union Road, GB-Cambridge CB? lEZ(UK), on quoting the full journal citation. (81 Twist angle T is defined by F. K. Winkler and J. D. Dunitz (see ref.
[2a]) as follows: 1 = 1'2 (wi + 02), where w , and o2 are torsion angles O-C4-N-C1 and C2-N-C4-C5, respectively. According to their definition, the value of the twist angle lies in the range -180" to 180". However, the larger the distortion, the nearer the value lies to 90" or -9O', on the other hand. the