Forbidden electrocyclic reactions can be more allowed than previously thought
By 
Ada McVean2025-03-05T08:58:00
Study suggests such reactions should instead be described as either ‘Woodward–Hoffmann favoured’ or ‘Woodward–Hoffmann disfavoured’
A computational study has challenged the long-standing notion that electrocyclic reactions can be neatly divided into being either ‘allowed’ or ‘forbidden’. ‘The energy difference between allowed and forbidden alternatives can sometimes be very small indeed,’ says Barry Carpenter, from Cardiff University in the UK. ‘In the smallest case that I found, it was less than half the barrier to the internal rotation of ethane.’