3.1. Molecular geometries:
A single CHD unit contains eight hydrogen atoms (four each in axial and
equatorial positions) attached to four carbon atoms. So, in a single CHD
molecule, there are eight C-H groups available that can potentially act
as H-bond donors. However, all the eight atoms don’t participate in
H-bond formation. During homo dimer formation, only the axial hydrogen
atoms (i.e. 2a, 4a and 6a in Figure 1) are known to act as H-bond donor.
During the cluster formation if both the axial and equatorial H-atoms
will participate, then the resulting geometry will be restricted for
further chain propagation. The geometry being restricted will not allow
for the formation of higher order clusters. So, only three axial C-H
groups participate in H-bonding during cluster formation. The geometries
involving the mentioned C-H groups participated in H-bond formation will
lead for higher order cluster formation.
The numbering of the donor C-H groups has been done according to their
gas phase acidity values. The group having the highest gas phase acidity
has been named as donor1. Gas phase acidity of the group 2a was found to
be -344.2 kcal mol-1, whereas the same for group 4a
and 6a were found to have equivalent gas phase acidity value i.e.-367.9
kcal/mol. Therefore the naming follows donor1 for group 2a, donor2 and
donor3 for 4a and 6a respectively. Also the naming of the H-bonds
present are according to the naming of these groups. H-bond1 (HB1),
H-bond2 (HB2) and H-bond3 (HB3) are bonding between C=O group with the
hydrogen of donor1, donor2, and donor3 respectively.