The electronic structure of five conformers of 2-chloroethanol was studied by ab initio calculations at B3LYP and MP2 levels of theory with aug-cc-pVTZ basis set. The existing hydrogen bond and hyperconjugation effects on the stability of 2-chloroethanol conformers were discussed on the base of natural bond orbital analyses. The result exhibits that hyperconjugation is the main factor to determine the stability of conformers. Such effects on the electron wavefunctions of the highest-occupied molecular orbital （HOMO） of different conformers are demonstrated with electron momentum spectroscopy, exhibiting the obviously different symmetries of the HOMO wavefunctions in momentum space.
