Page - (000020) - in Biomedical Chemistry: Current Trends and Developments

1 x 2s + 2 x 2p 3 x sp2 1 x 2s + 2 x 2p 2 x sp All of the hybrid orbitals may be used to form σ (sigma) molecular orbitals by fusion with s or with other hybrid orbitals from other atoms (according to Molecular Orbital Theory). If there are remaining 2p orbitals in the carbon atoms (in the case of sp2 and sp hybrid orbitals) they are used to form π (pi) molecular orbitals by lateral combination with other adjacent 2p orbitals (Fig. 1.1.1). A simple bond is formed with a single σ-bond; the double bond is formed with a σ-bond and a π-bond; the triple bond is formed with a σ-bond and two π-bonds. Figure 1.1.1: A simplified representation of the spatial distribution of two adjacent p orbitals (a) and their combination into a π bond (b) between two sp2 carbon atoms. The π-bonds in a triple bond would be along orthogonal planes to each other. These hybridisations have several consequences, such as the electron density of a π-bond lying above and below the plane of the bonding atoms (Fig. 1.1.1), resulting in greater exposure for a reaction. Simultaneously, with the increasing s character of the hybrid orbital: – the formed bond length decreases;