Smell of walnuts

Walnuts are an odd fruit…nut… I plucked one from a tree on a recent dogwalk and when I cut off the fleshy out coating this evening to get to the kernel the overwhelming odour it exuded took me right back to the first flat I shared with Mrs Sciencebase where we had a walnut tree. Of course, unprocessed you have to remove that outer flesh and then crack the soft(ish) shell and then remove the bitter pith to eat the deliciously sweet kernel. The pith is very bitter and to be honest, I don’t enjoy ripe walnuts of the kind you used to get on a Walnut Whip and that are ubiquitous in a Christmas bag of mixed nuts.

Anyway, I was curious as to what the odour of slightly unripe walnuts is musing with a chemist’s brain that there might be a single compound responsible. There isn’t, there’s a whole collection of compounds that give walnuts their distinctive scent: pinocarvone, aa-aldehyde canfolenic, chrysanthenone, trans-pinocarveol, trans-ßß-farnesene, trans-ßß-verbenol, aa a-terpinene and aa a-terpinolene (the a and aa in prefixes should be alphas, and if the betas aren’t translating, they’re betas).

Intriguingly, a quick Google on walnuts revealed some work on using these various compounds and pest insect lure compounds as alternatives to conventional pesticides, more on that here. It’s too late in the evening for me to ChemDraw those compounds (i.e. it is well past beer o’clock and I have a curry bubbling in the pan) but I may update this post if there is demand from botanical/natural product chemist friends who don’t believe I could produce the chemical structures of all those alphas and betas…