Carbocation bond angles

NotE, howEVEr, that an X-ray structurE analysis of thE stablE, ctystallinE carbocation 3,5,7-trimEthyladamantyl showEd thE 3-coordinatE C(l) atom as a considErably flattEHEd pyramid 21pm abovE thE planE of thE 3 adjacEnt C atoms and with bond anglES 120°, 118° and 116° (X = 354°). T. LaubE, Angew. Chem. Int. Edn. Engl. 25, 349-51 (1986). 

A recent X-ray characterization of the cyclopentyl cation 33 generated with methyl carboranes has shown a perfect planar structure around the carbocation center [bond angles CH3-C+-CH2= 124.9 and 125.2°, CH2-C+-CH2= 109.9° bond distances CH3-C+ = 1.46 A, CH2-C+ = 1.45 A).123... 

C is correct Carbocations are sp2 hybridized and should be planar with bond angles of 12CP. 

A carbocation (also called a carbonium ion or a carbenium ion) is a species that contains a carbon atom bearing a positive charge. The positively charged carbon atom is bonded to three other atoms, and it has no nonbonding electrons, so it has only six electrons in its valence shell. It is sp2 hybridized, with a planar structure and bond angles of about 120°. For example, the methyl cation (+CH3) is planar, with bond angles of exactly 120°. The unhybridized p orbital is vacant and lies perpendicular to the plane of the C—H bonds (Figure 4-13). The structure of +CH3 is similar to the structure of BH3, discussed in Chapter 2. 

A carbocation has three bonded groups and is trigonal, sp2 hybridized, and has 120 °bond angles. The empty orbital is the unhybridized p-orbital. 

Carbocations prefer s/r hybridization and 120° bond angles. As the ring gets smaller, the deviation from 120° increases, thereby destabilizing the carboca-tion. (Compare Problem 22 of Chapter 6.)... 

Figure 2.11 Preference of carbocations for planar geometry (120° inter-bond angles).

Carbocations prefer a planar geometry any structural feature that interferes or prevents the attainment of 120° inter-bond angles will hinder (retard) carbocation formation (Figure 2.11). 

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