Table 3. Calculated Strain Energies (kcal/mol) for the Studied Compounds Estimated at the MP2 and the M06-2X Level of Theory.

CHP	azepane	oxepane	thiepane	FCHP	ClCHP	BrCHP
MP2 Level
6.38 kcal/mol	5.09 kcal/mol	5.77 kcal/mol	5.82 kcal/mol	6.55 kcal/mol	7.14 kcal/mol	7.04 kcal/mol
M06-2X Level
5.69 kcal/mol	5.33 kcal/mol	5.12 kcal/mol	6.17 kcal/mol	5.97 kcal/mol	6.77 kcal/mol	6.77 kcal/mol