Condensation of 1, 3-diamines with aldehydes or ketones gives rise to two major products, the hexahydropyrimidine and the bisimine. Experimental studies of the reaction between a range of aromatic aldehydes and 1, 3-diaminopropane or 1, 3-diamino-2-propanol establish that the hexahydropyrimidine is favoured by the less nucleophilic amine and by the presence of electron withdrawing groups on the aryl ring of the aldehyde. Calculations ...