Riemer-Tiemann reaction introduces an aldehyde group, on to the aromatic ring of phenol, ortho to the hydroxyl group. This reaction involves electrophilic aromatic substitution. This is a general method for the synthesis of substituted salicylaldehydes as depicted below.

The electrophile in this reaction is :

Riemer-Tiemann reaction introduces an aldehyde group, on to the aromatic ring of phenol, ortho to the hydroxyl group. This reaction involves electrophilic aromatic substitution. This is a general method for the synthesis of substituted salicylaldehydes as depicted below.

The structure of the intermediate I is

When benzene sulphonic acid and $p$-nitrophenol are treated with $\mathrm{NaHCO}_3$, the gases released respectively are

(I) 1,2-Dihydroxybenzene

(II) 1,3-Dihydroxybenzene

(III) 1,4-Dihydroxybenzene

(IV) Hydroxy benzene

The increasing order of boiling points of the above mentioned alcohols is