Molecular orbitals methyl chloride

One way to investigate the electrophilic properties of these molecules is to examine the orbital that each uses to accept electrons from a nucleophile. This orbital is the lowest-unoccupied molecular orbital (LUMO). Examine the LUMO for methyl acetate (Z=OCH3), acetaldehyde (Z=H), N,N-dimethylacetamide (Z=N(CH3)2) and acetyl chloride (Z=C1) (acetaldehyde is not a carboxylic acid derivative, but is included here for comparison). What is the shape of the LUMO in the region of the carbonyl group Is it a o or 7U orbital Is it bonding or antibonding What other atoms contribute to the LUMO Which bonds, if any, would be weakened when a nucleophile transfers its electrons into the LUMO ... 

Now, examine the orbital on cyclohexanone lithium enolate most able to donate electrons. This is the highest-occupied molecular orbital (HOMO). Identify where the best HOMO-electrophile overlap can occur. Is this also the most electron-rich site An electrophile will choose the best HOMO overlap site if it is not strongly affected by electrostatic effects, and if it contains a good electron-acceptor orbital (this is the lowest-unoccupied molecular orbital or LUMO). Examine the LUMO of methyl iodide and trimethylsilyl chloride. Is backside overlap likely to be successful for each The LUMO energies of methyl iodide and trimethylsilyl chloride are 0.11 and 0.21 au, respectively. Assuming that the lower the LUMO energy the more effective the interaction, which reaction, methylation or silylation, appears to be guided by favorable orbital interactions Explain. 

Ab initio molecular orbital calculations are being used to study the reactions of anionic nucleophiles with carbonyl compounds in the gas phase. A rich variety of energy surfaces is found as shown here for reactions of hydroxide ion with methyl formate and formaldehyde, chloride ion with formyl and acetyl chloride, and fluoride ion with formyl fluoride. Extension of these investigations to determine the influence of solvation on the energy profiles is also underway the statistical mechanics approach is outlined and illustrated by results from Monte Carlo simulations for the addition of hydroxide ion to formaldehyde in water. 

Fig. 1.59 The filled molecular orbitals and the lowest unfilled molecular orbital of methyl chloride...

We can understand the tendency for the radical anion [H3C—Cl ] to dissociate to a methyl radical and chloride ion by referring to Figure 14.3, which illustrates the destabilizing anh-bonding interaction between carbon and chlorine in the highest occupied molecular orbital (HOMO) of the radical anion. This results in a much weaker bond and a C—Cl distance, calculated to be 324 pm, that is longer than that of methyl chloride itself (181 pm). 

Reactions of methyl(vinyl)iodonium ion and its jS-substituted derivatives with chloride ion have been treated by ab initio molecular-orbital calculations (MP2, double-zeta -I- d level). Transition states for 5n2, ligand-coupling substitution (LC), and -elimination ifE) were found. In the gas phase, the barrier to LC is usually the lowest, but the relative barriers for S 2 and change with the substituents. Solvent effects were treated in terms of a dielectric continuum model and found to be large on 5 n2 but small on LC. 

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