Acetyl chloride, electrostatic potential

DNA sequencing and. 1113 Electrospray ionization (ESI) mass spectrometry, 417-418 Electrostatic potential map, 37 acetaldehyde, 688 acetamide, 791,922 acetate ion. 43. 53, 56, 757 acetic acid. 53. 55 acetic acid dimer, 755 acetic anhydride, 791 acetone, 55, 56. 78 acetone anion, 56 acetyl azide, 830 acetyl chloride, 791 acetylene. 262 acetylide anion, 271 acid anhydride, 791 acid chloride, 791 acyl cation, 558 adenine, 1104 alanine, 1017 alanine zwitterion, 1017 alcohol. 75 alkene, 74, 147 alkyl halide, 75 alkyne. 74... 

Electronically, we find that strongly polarized acid derivatives rea more readily than less polar ones. Thus, acid chlorides are more reacti. than esters, which are more reactive than amides, because the electronegative chlorine polarizes the carbonyl group more strongly than does an alkoxy group or an amino group. These polarity differences can be seen in electrostatic potential maps such as those of iV,iV-dimethylacetamide and acetyl chloride shown below. The carbonyl carbon is less positive and less reactive in the amide than in the acid chloride. 

Figure 20.1 shows the structures and electrostatic potentials of the various derivatives of acetic acid-acetyl chloride, acetic anhydride, ethyl acetate, acetamide, and acetonitrile. Like the other carbonyl-containing compounds that we ve studied, acyl chlorides, anhydrides, esters, and amides all have a planar arrangement of bonds to the carbonyl group. 

Electrostatic potential map acetamide. 111 acetate ion, 741, 742 acetic acid, 739, 742 acetic anhydride. 111 acetone enol, 701 acetonitrile. 111 acetyl chloride, 114, 111 acetylene, 339, 342 amino acids, 1053 aniline, 862 benzene, 398 benzyne, 930... 

The key reactive intermediates in Friedel-Crafts acylations are acylium cations. These spedes can be formed by the reaction of acyl halides with aluminum chloride. The Lewis add initially coordinates to the carbonyl oxygen because of resonance (see Exadse 2-11). This complex is in equilibrium with an isomer in which the aluminum chloride is bound to the halogen. Dissociation then prodnces the acylium ion, which is stabilized by resonance and, unlike alkyl cations, is not prone to rearrangements. As shown in the electrostatic potential map of the acetyl cation in the margin, most of the positive charge (blue) resides on the carbonyl carbon. 

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