rming moiety which is methyl or ethyl, e.g. ##STR25## ??,??-acetylenic aldehydes or ketones, for example compounds containing a --C.tbd.C--CHO or --C.tbd.C--CO-- moiety; ??,??-acetylenic esters or thio- esters that have methyl or ethyl as their alkyl moiety, for example a compound containing a --C.tbd.C--COOR, --C.tbd.C--C(S)OR, --C.tbd.C--C(O)SR or --C.tbd.C--CSSR group in which R is an ester for