[greenteacup]

In my lab, we had to calculate the heat of formation of cyclohexane of these three conformations (chair, twist, & boat). Using the single point energy method (which calculated the heat of formation of the molecule exactly as I entered it without optimization), I got
chair = -35.190 kcal/mol
twist = -31.779 kcal/mol
boat = -31.406 kcal/mol

and the next question is "What is wrong with these, and how might this problem be corrected?" The problem is that I'm not sure what IS wrong with them..? I thought initially that maybe the chair was supposed to be less in absolute value than the twist & boat, but when I followed the hint it gave and used the equilibrium geometry method (which optimized it), it followed the same pattern with the chair conformation having the highest absolute value... so I'm not sure what's apparently wrong with it.

Any help is appreciated. Thanks in advance!