Intriguingly, similar but different to accounts of the literature for the appearance of 1, in particular, its colour, 6 also exhibits a yellow colour (Fig. ), and inasmuch as this furan technically has only one extra auxochromic oxygen than say, 1; this auxochromic impact on the conjugated system of 6, renders this molecule to fit into the literature descriptions of 1 (loc. cit.), which all seem to sit right with 6 both in 'structure & colour' (Fig. ). On another development, carbohydrazide 7 was serendipitously obtained in lieu of 6 via the action of hydrazine monohydrate on 5-nitro-2-furonyl chloride (ESI S6 †): the colour of 7 is again of particular importance, and reference has already been made to the correlation between purity of conjugated nitrofuranyl derivatives and their intrinsic colours (vide supra). With that borne in mind, we saw that the delocalisation of eight  electrons in 1 was responsible for its orangish colour; it also brought home to us that symmetry would influence the colour of conjugated molecules cf. lycopene and β-carotene: here again, 7 is not fully conjugated, but indeed symmetric. On the other hand, 7 possesses several nitrogen and oxygen auxochromes, which can donate their accessible lone pairs to the conjugated system so as to extend the electron delocalisation in the already established conjugated system. This effect together with the partial double bond character of semicarbohydrazide in the dimer facilitates its tautomerisation to give a more stable fully conjugated dimer 8 with 16 delocalised  electrons in its conjugated system (Scheme 4).