Hindered rotation in 1,2-dineopentyltetramethylbenzene

✍ Scribed by D.T. Dix; G. Fraenkel; H.A. Karnes; M.S. Newman

• Publisher: Elsevier Science
• Year: 1966
• Tongue: French
• Weight: 145 KB
• Volume: 7
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)72914-5

✦ Synopsis

1,2_Dineopentyltetramethylbenzene, I, is an extremely crowded mole-1 cule. We have found that the rate of rotation about the CA,-C& bonds is sufficiently slow to be measured by the methods of n.m.r. spectroscopy 233 . This is the first example of hindered rotatipn of alQ1 groups attached to a single benzene ring. The chemical shifts of the hydrogens obtained from a 5% solution in Ccl4 of I are as follows: 4 C(CHs)s, 9.16; CArCH3, 7.785, and 7.744; C& centered at 7.083, tau units respectively. The magnitudes of these shifts are unexceptional. However, by -30' the methylekhydrogens became magnetically nonequivalent. Their absorption then consists of a typical AR quartet where bAB = 0.240 ppm and JAR = 14.2 cps, see Figure la. With increasing temperature the AB quartet which remains centered at '7.083 tau collapses progressively to a single line by 80°, Figure la-f.