The ordering of the relative stabilities of adducts L · BH₃ for some common adducts is, according to L: Me₂O < THF < Me₂S < Me₃N < Me₃P < H‾. In addition to answering each of the following, indicate how you could use NMR spectroscopy to confirm your proposals.

(a) What happens when Me₃N is added to a THF solution of THF·BH₃?

(b) Will Me₂O displace Me₃P from Me₃P·BH₃?

(c) Is [BH₄]‾ stable in THF solution with respect to a displacement reaction?

(d) Suggest what may be formed when Ph₂PCH₂CH₂PPh₂ is added to a THF solution of THF·BH₃, the latter remaining in excess.