Hi – the issue is not that nitrogen can’t be on a bridgehead (it can – see compounds like quinuclidine and DABCO which are good bases) it’s that the lone pair on the nitrogen will not have good overlap with the p orbital on an adjacent carbon, which means that bridgehead amides will have very little C-N double bond character.

Please explain that in a particular compound if Nitrogen is located at bridgehead position so is it able to donate it’s lone pair ? Is it basic ?
And if basic then you said sp2 carbon cannot be formed on bridgehead position so how and why nitrogen is able to donate it’s lone pair easily .

Source:(JEE MAIN 2025 4th April Evening Shift)
Please tell me sir

Good question. I don’t think the new paper changes things all that much, but it’s a good addition to the literature.

I think the message from the new paper is that and olefins do form, but they just happen to be very unstable at low temperature and can be trapped.

Kind of like how cyclobutadiene can be formed at very low (35 K) temperatures but spontaneously dimerizes.

McDermott, L. et al. Science 386, eadq3519 (2024). https://doi.org/10.1126%2Fscience.adq3519
Chan, T. H. & Massuda, D. J. Am. Chem. Soc 99, 936–937(1977). https://doi.org/10.1021%2Fja00445a042

Fixed. Thanks Pragna!

Absolutely not! No backside attack possible.

2-quinuclidone, or 1-azabicyclo[2.2.2]octan-2-one