Cycloheptane, strain energy

This can be thermodynamically explained in that the ring-strain energy is less suitable for the formation of cyclononane from cyclodecane than the formation of cycloheptane from COA (or cyclohexane from cycloheptane) [144]. Overall, these reactions successfully yielded the ring expansion, ring contraction, but this system suffers from the formation of polymers as major products [145]. 

There is also a boat-like conformation, 49C, but the flat part of the seven-membered ring has diminished transannular strain because the hydrogen atoms are a little further apart. The strain energies for chair cycloheptane and boat cycloheptane are close, and one does not greatly predominate over the other. There are several other conformations for cycloheptane, as there are for cyclohexane, because the size and flexibility of the ring has increased however, at this point, no other conformations for cycloheptene will be discussed. 

Verify the strain energy shown in Table 3.8 for cycloheptane. 

D is correct. Cycloheptane has the most ring strain and is at the greatest energy level. It will produce more heat per mole than methane or ethane because it is a larger molecule. 

Rings larger than six-membered are always puckered unless they contain a large number of sp atoms (see the section on strain in medium rings, p. 223). The energy and conformations of the alkane series cycloheptane to cyclodecane... 

This flattening is due to the presence of an odd niimber of carbons in the ring and it means that there will be some torsion strain due to eclipsing bonds and atoms in this form of cycloheptane. Some twisting of the ring can occur to relieve this strain, but such pseudorotation may increase strain elsewhere in the molecule. This increase in strain makes conformations 49A and 49B for cycloheptane higher in energy than the chair conformations of cyclohexane. 

---