The first bond formed between any two atoms is a sigma bond. Stability of hydrocarbons. This is the same as one unit of unsaturation. Something is chiral if it has no plane of symmetry, and if its mirror image is not superimposable on the original. The relationship between a chiral compound and its non-superposable mirror image is enantiomers .
Enantiomers have different properties in chiral environments .
Diastereomers have different physical and chemical properties from each other . These diastereomers can be separated by standard achiral physical methods such as chromatography or crystallization. You then trace from priority 1 to 2 to 3. Alternately, the heats of combustion per CH 2 can be used. The corresponding energy profile is on page 205.