Question

Please comments on the difference between methyllithium and methyl bromide. Be sure to address both structure (bonding, polarity, etc.) and reactivity aspects

Answer 1

Solution

Methyl lithium

Methyllithium is the simplest organolithium reagent with the empirical formula CH₃Li. This s-block organometallic compound adopts an oligomeric structure both in solution and in the solid state.

Methyllithium is both strongly basic and highly nucleophilic due to the partial negative charge on carbon .

Structure

Two structures have been verified by single crystal X-ray crystallography as well as by ⁶Li, ⁷Li, and ¹³C NMR spectroscopy. The tetrameric structure is a distorted cubane-type cluster, with carbon and lithium atoms at alternate corners. The Li---Li distances are 2.68 Å, almost identical with the Li-Li bond in gaseous dilithium. The C-Li distances are 2.31 Å. Carbon is bonded to three hydrogen atoms and three Li atoms. The nonvolatility of (MeLi)₄ and its insolubility in alkanes results from the fact that the clusters interact via further inter-cluster agostic interactions. In contrast the bulkier cluster (tertiary-butylLi)₄, where intercluster interactions are precluded by steric effects, is volatile as well as soluble in alkanes.

Bonding amd Reactivity :

These clusters are considered "electron-deficient," that is, they do not follow the octet rule because the molecules lack sufficient electrons to form four 2-centered, 2-electron bonds around each carbon atom, in contrast to most organic compounds.

Polarity :

The [CH₃^-] group, a methyl anion, has covalent bonds between carbon and hydrogen. Though there is no significant bond polarity to a C-H bond there is a molecular polarity to the anion because of the negative charge placed on carbon. The attraction of the Li⁺ cation to CH₃^- is essentially ionic.

Methyl bromide :

Bromomethane, commonly known as methyl bromide, is an organobromine compound with formula CH₃Br.

This colorless, odorless, nonflammable gas is produced both industrially and biologically.

Structure:

It has a tetrahedral shape and it is a recognized ozone-depleting chemical.

Carbon forms four tetrahedral bonds with other elements which are equally spaced around the central carbon atom

Polarity:

However, when you replace one of the hydrogens with a bromine, the situation has become unbalanced with a shift of the electron pair between the C & the Br shifting toward the Br. This shift results in the methyl bromide being a polar molecule.

All the best buddy please upvote it