Three types of isomers of C 2 H 3 OLi (lithium enolate, CH 2 =CH(OLi); acyl lithium, CH 3 -C(C=O)Li; a model of unsaturated α-lithio-ether, CH 2 =C(OH)Li) were investigated carefully. Structure 2 will be the valuable structure in stereoselective synthesis for lithium enolates. In some conditions, acyl lithium CH 3 -C(=O)Li can be dipolymerized via carbene intermediate 7. The model of unsaturated α-lithio-ether CH 2 =C(OH)Li has dual reactivity: structure 13 is the reaction intermediate when CH 2 =C(OH)Li serves as an acyl anion equivalent; structure 10 is the real reaction structure for CH 2 =C(OH)Li serving as a carbenoid, and the configuration of the central C will be inverted in the reaction route. Furthermore, CH 2 =C(OH)Li will dominantly react like a 'carbanion'. Mutation among isomers of different types is almost impossible.