The mechanisms for the insertion reactions of alkylidenecarbenes with CH3O-H have been investigated at the B3LYP/6-311G(d,p) level of the theory. According to our model calculations these insertion reactions will easily yield vinyl ether products and for a given single substituted alkylidenecarbene will yield cis-trans-isomer mixture. Moreover the reactivity of alkylidenecarbene decreases in the order: HFC=C > HClC=C > HBrC=C > H(CH3)C=C > H2C=C. Furthermore, a configuration mixing model based on the work of Pross and Shaik is used to rationalize the computational results. (c) 2005 Elsevier B.V. All rights reserved.