Carbenes of different electron configurations and geometrical shapes. <br><p><b>Left</b>: Singulet carbene. The central carbon is sp<sup>2</sup>-configured. Two sp<sup>2</sup> orbitals are involved in covalent bonds with the two substituents. Both electrons occupy the third sp<sup>2</sup> orbital and the remaining p-orbital is not occupied. This is the typical shape of carbenes with substituents that have a free electron pair adjacent to the central carbon, for instance :CCl<sub>2</sub>. <br><b>Center</b>: Triplet carbene, bent. The central carbon is again sp<sup>2</sup>-configured, but the two additional electrons occupy both the third sp<sup>2</sup> orbital and the remaining p-orbital. This is the typical shape of carbenes with substituents lacking free electron pairs. Examples are :CH<sub>2</sub> and :CHPh. <br></p>
<b>Right</b>: Triplet carbene, straight. The central carbon is sp-configured, resulting in a straight geometry (like in alkynes). The two free electrons occupy the two degenerate p-orbitals. This form is less common than the bent variants.
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