Primary and Secondary Alcohols in the Condensed Phase

When GC had become available as a powerful tool for the analysis of trace components, photolysis experiments with saturated alcohols were resumed by Yang and his group (125,126). 

They investigated methanol, ethanol, isopropanol (125), and n-pentanol (126). Photolysis became negligible when the 185 nm line of the Hg-low-pressure arc was filtered off by means of a vycor quartz tube. This is as expected from the characteristics of alcohol spectra, and is in contrast to the findings of Sullivan and Koski who observed ESR signals from samples of 

TABLE 5. Quantum yields of key products in the UV photolysis (x 185 nm) of liquid primary and secondary alcohols. 

In the photolysis of 0-deuterated alcohols some (about 15 - 20%) H2 is also formed. This could be caused by elimination of carbon bound hydrogen atoms (e.g., reaction 4), or the formation of molecular hydrogen and a carbene. Carbenes have been shown to be intermediates in the photolysis of hydrocarbons 

Another route of hydrogen elimination occurs with the formation of epoxides. It has been shown (137) that only those alcohols give epoxides in which the hydrogen bound to the oxygen is suitably positioned relative to the hydrogen on the g-carbon atom. This is the case, for example, with isopropanol but not with n-propanol where the hydroxyl group can orient itself such as to yield to steric repulsion by the alkyl chain (c.f. the Newman projections [2] and [3]). 

---