Simple Aliphatic Ketoximes

Consider equation 23 that relates the oximes to the corresponding ketones. 

For the two aldehydes discussed in the previous section (R, R = H R = Me, R = Hep), the reaction is thermoneutral in the gas phase. Thermoneutrality would also be expected for ketones, but which ketone/oxime should be the standard for comparison In the gas phase there are two possibilities acetone/acetone oxime and cyclohexanone/cyclohexanone oxime. The latter pair may be assumed to be essentially strainless, or at least that their strain energies are very much the same. The assumption is borne out by substituting these two pairs into equation 23 (R, R = Me R R = — (CH2)5—) and finding that the enthalpy of reaction is only 1.2 kJ moE, essentially thermoneutral. Comparing the Cg species with the cyclohexyl species (RR = —(CH2)s- R /R = Me/Hex, Et/Pen, Pr/Bu), the enthalpies 

There remains to be discussed butanone oxime, for which there is an enthalpy of formation value only in the liquid phase. The enthalpy of reaction 23 (RR = —(CH2)5— R = Me, R = Et) is +11.8 kJmoH. The enthalpy of formation of butanone oxime would seem to be ca 12 klmoE too negative. 

Finally, assuming a linear relationship between the enthalpies of formation and carbon number for the 2-alkanone oximes, and a gas phase methylene increment of —20.7 kJ mol , the same as for the 2-alkanones, the enthalpies of formation of 2-butanone and 2-octanone oximes would be —82.5 and —166.3 kJmoH, respectively. The latter value is within 1 kJmoE of that derived from equation 23. 

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