Question

In Chapter 6, we study a group of organic cations called carbocations. Following is the structure of one such carbocation, the tert-butyl cation. CC(C)=C(C(=O)O)c1ccccc1 (a) How many electrons are in the valence shell of the carbon bearing the positive charge? (b) UsingVSEPR, predict the bond angles about this carbon. (c) Given the bond angle you predicted in (b), what hybridization do you predict for this carbon?

Short answer

Answer: In the tert-butyl cation, the positively charged carbon has 3 valence electrons, the expected bond angles are approximately 120°, and its predicted hybridization is sp2.

Step-by-step solution

Draw the Lewis structure of the tert-butyl cation

To answer the questions, we first need to draw the Lewis structure of the tert-butyl cation. The tert-butyl cation has the formula (CH3)3C+.

Identify the positive charge bearing carbon

The carbon atom that bears the positive charge is the central carbon atom in the molecule. It is surrounded by 3 methyl groups (CH3).

Determine the valence electrons of the positive charge bearing carbon (#question a#)

In a neutral carbon atom, there are 4 valence electrons. However, in the tert-butyl cation, the central carbon is positively charged and has lost one electron, so it now has only 3 valence electrons. (a) The carbon bearing the positive charge has 3 valence electrons.

Apply VSEPR theory to predict bond angles (#question b#)

VSEPR (Valence Shell Electron Pair Repulsion) theory can be used to predict the bond angles in a molecule. In the tert-butyl cation, the central carbon atom is surrounded by 3 methyl groups and does not have any lone pairs. According to VSEPR theory, these groups will be arranged so as to minimize repulsion, and the shape of the molecule will be trigonal planar. (b) Based on VSEPR theory, the bond angles around the central carbon atom are expected to be approximately 120°.

Predict the hybridization of the central carbon atom (#question c#)

The hybridization of an atom can be determined based on its electron-domain geometry. In the case of the tert-butyl cation, the electron-domain geometry around the central carbon atom is trigonal planar, which corresponds to sp2 hybridization. (c) The hybridization of the central carbon in the tert-butyl cation is predicted to be sp2.