SOME THERMOCHEMICAL PROPERTIES OF METHYL VINYL ETHER ALPHA-CHLOROETHYL METHYL ETHER AND IODOMETHYL METHYL ETHER . EVIDENCE FOR NONBONDED ELECTROSTATIC INTERACTIONS

The entropies of methyl vinyl ether (MVE, S°298 = 73.5 gibbs/mole) and α-chloroethyl methyl ether (CME, S°298 = 82.4 ± 2.1 gibbs/mole) have been calculated, respectively, by statistical mechanical methods, and from the measured equilibrium constant, Ka CH3OCHCICH3 ↔ HC1 + CH3OCH=CH2 (a). In the latter measurement, HC1 pressures were varied from 104.5 to 227.8 torr, and MVE from 28.57 to 213 torr. Log (Ka/atm) = [(34.0 ± 1.5)/4.576] - [(17.5 ± O.7)/⊖], where ⊖ = 2303RT in kilocalories/mole, and errors quoted are 95% confidence limits. Smoothing these values to ∆H = 17.0 kcal/mole by comparison with the similar equilibrium for ethyl vinyl ether leads to ∆Hf°298(CME) = –65.2 ± 1.2 kcal/mole. The heat of formation of iodomethyl methyl ether (∆Hf°298(IME) = –29.3 kcal/mole) was calculated from the equilibrium constant, Keq, at 566°K for the system CH3OCH3 + I2 ↔ HI + ICH2OCH3 (IME) and an assigned value for the entropy of the iodomethyl ether. I2 pressures were varied from 3.76 to 18.85 torr and dimethyl ether pressures from 39.62 to 592 torr. The temperature range was 515-631.60 K. °S°298(CME) was abnormally low by 1.9 gibbs/mole on comparison with isoelectronic. sec-butyl chloride, and ∆Hf°(CME) was abnormally stable by about 6.1 kcal/mole. ∆Hf°(IME) showed a similar enhanced stability of about 3 kcal/mole. Both of these values are shown to be consistent with an electrostatic interaction of the halogens with the terminal methyl group arising from the alternate polarity of bond dipoles. © 1969, American Chemical Society. All rights reserved.