Reflectance absorbance infrared (RAIRS) and thermal desorption (TPD) d
ata for methyl formate and ethyl formate chemisorbed on Ni(111) are fo
und to be consistent with surface coverage dependent rotational isomer
ization. The most stable gas phase rotameric forms of these molecules
are the (Z) or cis forms. However, the reflectance infrared data provi
de direct evidence for isomerization to the (E) or anti forms as their
surface coverages are increased. This rotational isomerization, aroun
d the C-O bond, is observed to occur at coverages less than half that
required to saturate the chemisorbed layers. In combination with infra
red integrated intensity data, the thermal desorption results indicate
that steric repulsion is responsible for the observed rotational isom
erization. It is argued that two factors contribute to a reduction of
the rotational barrier. First, steric repulsion is reduced continuousl
y along the (Z) to (E) rotational coordinate. Second, image dipole sta
bilization increases continuously along the (Z) to (E) rotational coor
dinate. A number of interesting parallels exist between the chemisorpt
ion properties of these three ester molecules on Ni(111) and the prope
rties of Lewis acid-carbonyl molecule adducts. These similarities will
be discussed briefly with reference to use of Lewis acids to achieve
stereoselective control in organic synthesis, and with reference to th
e issue of enantioselective heterogeneous catalysis.