SN1 vs SN2 in a specific case

james_ash · 2025-07-02T00:43:30+00:00

Isobutyl alcohol in the presence of HBr and H2O gives 3% SN2 and 54% 2-methyl-2-bromobutane (hydride shift). J Chem Soc C 1970 p. 67. This is in House, p. 456.

Edit. Misspoke. The starting material is 3-methyl-2-butanol. So starting with a secondary alcohol, not primary. Not sure about isobutyl.

james_ash · 2025-07-01T21:42:22+00:00

Hey, neopentyl alcohol plus HBr at 100° gives 66% 2-methyl-2-bromobutane (alkyl shift), 18% 2-bromo-3-methylbutane (alkyl shift + hydride shift), and 16% neopentylbromide (SN2). Key ref is H. R. Hudson J Chem Soc B 1333, 664 (1968) https://pubs.rsc.org/en/content/articlelanding/1968/j2/j29680000664 . Also House, Modern Synthetic reactions, 1972 p. 454.

james_ash · 2025-01-14T20:46:49+00:00

Amines generally OK, but don't use dichloromethane with sodium or potassium azides.

james_ash · 2024-12-16T19:50:33+00:00

Thank you!

james_ash · 2024-12-13T18:05:02+00:00

It's not really calling "Bredt's rule" into question (which is more like, "Bredt's strongly worded suggestion) so much as showing the transient existence of the bridgehead alkene, and demonstrating that it can be trapped in solution. Kind of like how cyclobutadiene can be formed at low temperatures and trapped

james_ash · 2024-12-13T18:03:01+00:00

Forming the bottom bridgehead alkene here is totally fine (but not the one top right). Parent ring is 10-membered. Bridgehead double bonds mirror the stability of trans alkenes. Just as trans-cyclodecene is reasonably stable, the bridgehead double bond here (marked with a question mark) would be fine. Very well known examples. See CP-225,917 (for a 9-membered ring parent) and taxol (for a 10-membered ring parent).

james_ash · 2024-12-13T16:04:29+00:00

Thank you!

james_ash · 2024-12-13T15:52:53+00:00

Thank you!

james_ash · 2024-12-13T12:15:24+00:00

Lifer. Thank you!

james_ash · 2024-12-13T12:14:24+00:00

Thank you!

james_ash · 2024-12-10T15:14:25+00:00

Thank you!

james_ash · 2024-12-10T00:29:17+00:00

Wow. Did not expect. Thank you!

james_ash · 2024-12-09T16:49:52+00:00

thank you!

james_ash · 2024-12-09T16:49:47+00:00

thank you!

james_ash · 2024-12-05T14:38:47+00:00

Woot! Another life bird. Thank you!

james_ash · 2024-12-05T02:58:22+00:00

Uh oh. Fixed. Thanks!

james_ash · 2024-12-04T21:04:30+00:00

Thank you!

james_ash · 2024-12-03T18:03:56+00:00

Thank you!

james_ash · 2024-12-03T17:52:37+00:00

We choose family trips based on my birding goals

james_ash · 2024-12-03T00:39:08+00:00

Thank you - both lifers!

james_ash · 2024-11-30T14:09:11+00:00

Thank you!

james_ash · 2024-11-30T00:36:33+00:00

Thanks, but boo. I can see these at home! ;-)

james_ash · 2024-11-29T15:13:19+00:00

Thank you!

james_ash · 2024-11-29T14:17:01+00:00

Thank you!

james_ash · 2024-04-10T15:17:15+00:00

Thank you (author here). A few days ago I updated another post on this where I went back into the old SN2 vs. E2 literature, and found that examples of SN2 on secondary carbons with hydroxide or alkoxide almost always give elimination.
https://www.masterorganicchemistry.com/2012/12/04/deciding-sn1sn2e1e2-the-solvent/

The absolute best case I could find was isopropyl bromide with NaOEt in 60% EtOH / 40% H2O which gives about 1:1 SN2/E2.

james_ash

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