Trimethylamine, bond angles

Trichloroacetic acid, pKa of. 759 Trifluoroacetic acid, pKa of, 756 Trifluoromethylbenzene, electrostatic potential map of, 565 Triglyceride, see Triacylglycerol, 1061 Trimethylamine, bond angles in, 919 bond lengths in, 919 electrostatic potential map of, 921 molecular model of, 919 Trimethylammonium chloride, IR spectrum of, 953 Trimethylsilyl ether, cleavage of, 627-628... 

In the case of the nitrogen compounds, the bond angles in the unprotonated species are rather close to those of the protonated species 97). Since there are only rather small geometric changes, the proton affinity of pyridine is close to that of trimethylamine. 

Figure 4.10. This creates a pyramidal geometry around nitrogen. H—N—H bond angles in ammonia are 107° experimental information shows a very similar C— N—C bond angle in trimethylamine.

Consider each of the following molecules in turn (a) dimethyl ether, (CH3)20 (b) trimethylamine, (CH3)3N (c) trimethylboron, (CH3)3B and (d) dimethylberyUium, (CH3)2Be. Describe the hybridization state of the central atom (i.e., O, N, B, or Be) of each molecule, tell what bond angles you would expect at the central atom, and state whether the molecule would have a dipole moment. 

The bond angles are what one would expect of a tetrahedral structure they are very close to 109.5°. The bond angles for trimethylamine, for example, are 108°. 

Bond angles, in 2-bromo-4 -dimethyl-amino-2-cyanostilbene 18 in trimethylamine 15 Bond lengths, in 2-bromo-4 -dimethyl-amino-2-cyanostilbene 18 in -iodoaniline 18 in trimethylamine 15 Bond order 22... 

Amines are like ammonia (Section 1.16B) in having a trigonal pyramidal shape. The C—N—C bond angles of trimethylamine are 108.7°, a value very close to the H—C—H bond angles of methane. Thus, for all practical purposes, the nitrogen atom of an amine can be considered to be sp hybridized with the unshared electron pair occupying one orbital (see below). This means that the unshared pair is relatively exposed, and as we shall see this is important because it is involved in almost all of the reactions of amines. 

The bonding in alkylamines is similar to the bonding in ammonia. The nitrogen atom is sp -hybridized, with the three substituents occupying three corners of a tetrahedron and the lone pair of electrons occupying the fourth corner. As you might expect, the C-N-C bond angles are close to the 109° tetrahedral value—108° in trimethylamine, for example. 

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