Acetamide, electrostatic potential

Electrostatic potential maps of a typical amide (acetamide) and an acyl azide (acetyl azide) are shown. Which of the two do you think is more reactive in nucleophilic acyl substitution reactions Explain. 

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... 

P. Cieplak and P. Kollman, /. Comput. Chem., 12, 1232-1236 (1991). On the Use of Electrostatic Potential Derived Charges in Molecular Mechanics Force Field. The Relative Solvation Free Energy of Cis- and Tri2ws-N-Methyl-Acetamide. 

Figure 1 Contour map of the negative of the molecular electrostatic potential for acetamide at the HF/3-21G( ) level calculated from the full molecular wavefunction. Shading indicates approximate value of the potential in the region. Thus, the MEP near the oxygen is negative, and the MEP near the amide hydrogens (not shown) is positive. The basis set has polarization functions only on second-row atoms.

Figure 2 Contour map of the negative of the molecular electrostatic potential for acetamide at the HF/S-ZIGI ) level calculated using the monopole approximation and the CHELP charges. Scale same as in Figure 1.

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. 

By comparison of the calculated electrostatic potentials (77) of trans-2-butene and 2-fluoro-2(Z)-butene with N-methyl acetamide as simple models of the peptidic bond and its isosteres (see figure 1) the fluoroolefin clearly is the better replacement of the amide bond, since it not only mimics its steric but also, at least in part, its electronic feature. Calculating dipole moments Abraham (73) came to similar results, but attempts to synthesize the corresponding dipeptide isostere 2 have been until now unsuccesful (14). As part of our ongoing program in fluoroorganic chemistry we developed two general methods for the preparation of these compounds. 

Figure 1. Dreiding and CPK representation (standard geometries) and electrostatic potential profiles of N-methyl acetamide, trans-2-butene and 2-fluoro-2(Z)-butene...

Figure 6 Calculated HF/ST0-5G electrostatic potential on the molecular surface of acetamide (24). Projections of bonds are indicated by solid black lines. Three ranges of V(r) are depicted lightest shading is for V(r) < 0 kcal/mol darkest is for 0 < V(r) < 20 kcal/mol intermediate is for V(t) > 20 kcal/mol.

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 difference in positive-charge distribution in an amide that accepts a proton on its oxygen or its nitrogen atom can be visualized with electrostatic potential maps. Consider the electrostatic potential maps for acetamide in its O — H and N — H protonated forms shown below. On the basis of the electrostatic potential maps, which protonated form appears to delocalize, and hence stabilize, the formal positive charge more effectively Discuss your conclusion in terms of resonance contributors for the two possible protonated forms of acetamide. 

Fig. 2.5a, b. Maps of the electrostatic potential of 2-formylamino acetamide obtained in a ab initio and b CNDO/2 calculations [50]. (Reproduced with permission from Kluwer Academic Publishers)... 

Figure 20.2 Calculated electrostatic potential maps (calibrated to the same charge scale) for ethylamine and acetamide. The map for ethylamine shows localization of negative charge at the unshared electron pair of nitrogen. The map for acetamide shows most of the negative charge at its oxygen atom instead of at nitrogen, due to the electron-withdrawing effect of the carbonyl group.

Electrostatic potential maps of (a) acetamide and Cb) methylamine are shown. Which has the more basic nitrogen atom Which has the more acidic hydrogen atoms ... 

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