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.