CHAPTER TWENTY-TWo Amines unshared electron pair on nitrogen occupies an sp-hybridized orbital. This lone pair is involved in reactions in which amines act as bases or nucleophiles. The graphic that You can opened this chapter is an electrostatic potential map that clearly shows the concentration cluding its electros of electron density at nitrogen in methylamine tial, in more detail By Modeling Arylamines: Aniline, like alkylamines, has a pyramidal arrangement of bonds around nitrogen, but its pyramid is somewhat shallower. One measure of the extent of this flat tening is given by the angle between the carbon-nitrogen bond and the bisector of the l80° Methylamine O=cHNH) For sp-hybridized nitrogen, this angle(not the same as the c-N--H bond angle)is 125, and the measured angles in simple alkylamines are close to that. The correspond ing angle for sp- hybridization at nitrogen with a planar arrangement of bonds, as in amines is discussed in an arti. amides, for example, is 180. The measured value for this angle in aniline is 142.5, sug cle entitled "What Is the gesting a hybridization somewhat closer to sp than to sp Geometry at Trigonal Nitro. gen?in the January 1998 is- The structure of aniline reflects a compromise between two modes of binding the nitrogen lone pair(Figure 22.3). The electrons are more strongly attracted to nitrogen Chemical Education, pp when they are in an orbital with some s character--an sp-hybridized orbital, for exam- ple--than when they are in a p orbital. On the other hand, delocalization of these elec trons into the aromatic T system is better achieved if they occupy a p orbital. A p orbital of nitrogen is better aligned for overlap with the p orbitals of the benzene ring to form a) FIGURE 22. 3 Electrostatic potential maps of the aniline in which the geometry at nitrogen is(a)nonplanar and(b)planar. In the nonplanar geometry, the unshared pair occupies an brid orbital of nitrogen. The region of highest In the planar geometry, nitrogen is sp 2-hybridize the electron pair is delocalized between p orbital of nitrogen and the t system of the he region of highest electron density in( b) encompasses both the ring and nitrogen the actual structure combines features of both; nitro- n adopts a hybridization state between sp and Back Forward Main MenuToc Study Guide ToC Student o MHHE Websiteunshared electron pair on nitrogen occupies an sp3 -hybridized orbital. This lone pair is involved in reactions in which amines act as bases or nucleophiles. The graphic that opened this chapter is an electrostatic potential map that clearly shows the concentration of electron density at nitrogen in methylamine. Arylamines: Aniline, like alkylamines, has a pyramidal arrangement of bonds around nitrogen, but its pyramid is somewhat shallower. One measure of the extent of this flat￾tening is given by the angle between the carbon–nitrogen bond and the bisector of the H±N±H angle. For sp3 -hybridized nitrogen, this angle (not the same as the C±N±H bond angle) is 125°, and the measured angles in simple alkylamines are close to that. The correspond￾ing angle for sp2 hybridization at nitrogen with a planar arrangement of bonds, as in amides, for example, is 180°. The measured value for this angle in aniline is 142.5°, sug￾gesting a hybridization somewhat closer to sp3 than to sp2 . The structure of aniline reflects a compromise between two modes of binding the nitrogen lone pair (Figure 22.3). The electrons are more strongly attracted to nitrogen when they are in an orbital with some s character—an sp3 -hybridized orbital, for exam￾ple—than when they are in a p orbital. On the other hand, delocalization of these elec￾trons into the aromatic system is better achieved if they occupy a p orbital. A p orbital of nitrogen is better aligned for overlap with the p orbitals of the benzene ring to form ≈125 Methylamine (CH3NH2) Aniline (C6H5NH2) Formamide (OœCHNH2) 142.5 180 862 CHAPTER TWENTY-TWO Amines The geometry at nitrogen in amines is discussed in an arti￾cle entitled “What Is the Geometry at Trigonal Nitro￾gen?” in the January 1998 is￾sue of the Journal of Chemical Education, pp. 108–109. (a) (b) FIGURE 22.3 Electrostatic potential maps of the aniline in which the geometry at nitrogen is (a) nonplanar and (b) planar. In the nonplanar geometry, the unshared pair occupies an sp3 hy￾brid orbital of nitrogen. The region of highest electron density in (a) is associated with nitrogen. In the planar geometry, nitrogen is sp2 -hybridized and the electron pair is delocalized between a p orbital of nitrogen and the system of the ring. The region of highest electron density in (b) encompasses both the ring and nitrogen. The actual structure combines features of both; nitro￾gen adopts a hybridization state between sp3 and sp2 . You can examine the structure of methylamine, in￾cluding its electrostatic poten￾tial, in more detail on Learning By Modeling. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website