198 Topics in Current Chemistry Editorial Board: A. de Meijere KN ...

10 J.P. Glusker
The forces here have some directionality, evidenced by the retention of the
PAH packing arrangement in both the crystal structure of a PAH alkylating
agent and that of its adduct with a tripeptide, shown in Fig. 3. In spite of the presence
of hydrophilic peptide groups in the adduct, the aromatic rings pack in
essentially the same manner. Similarly in the cinnamic acids, close approaches
of carbon-carbon double bonds in the crystalline state can, on photoactivation,
lead to cyclobutane products, as diagrammed in Fig. 4 [14]. These examples suggest
that there can be some directionality in C◊◊◊C and C◊◊◊H interactions in
crystals. The forces between molecules containing oxygen in addition to carbon
and hydrogen, however, are much more complicated, especially if hydrogen
bonding is possible. It is therefore still necessary to study the results of crystal-
a
b
Fig. 3 a , b. Crystal packing of aromatic groups in an anthracene derivative and in a tripeptide
alkylated by this derivative [14]: a chemical formulae of (left) the alkylated peptide and (right)
the alkylating agent; b stereoview of packing in chloromethylanthracene. (H omitted)