# Stereochemical aspect of heating of cyclohexane-1,2-diol

Does stereochemistry play any role in the heating of Cyclohexane-1,2-diol?

If I remember correctly, different products are formed depending on whether the diol is cis or trans. (I think the products are cyclohexanone and cyclopentanecarbaldehyde). Please clarify this along with the reason why different products are formed depending on the stereochemistry.

The reaction you are thinking of is likely the thermal decomposition of the cyclic sulfites prepared from the cis- and trans-diols. Here is a link to the abstract.

In both reactions $\ce{SO2}$ is extruded. Whichever group on the vicinal carbon that is lined up in an anti-periplanar fashion to the departing oxygen is the group that migrates. This is because the antiperiplanar geometry allows for good orbital overlap during the migration; if a choice is available then hydrogen migrates in preference to an alkyl group just as with carbocations. In the cis-isomer, the vicinal hydrogen is properly aligned (I darkened the affected bonds to highlight the geometric arrangement), its migration produces cyclohexanone. In the trans-isomer, only a $\ce{C-C}$ bond in the cyclohexane ring is properly aligned, its migration produces cyclopentanecarbaldehyde.

• Is this also valid for cyclohexane-1,2-diol? – Binary Geek Apr 18 '15 at 2:35
• No, that's why I think this must be the reaction you are remembering. It gives the products you mentioned and the sulfites are prepared from the two cyclohexane-1,2-diols.. Cyclohexane-1,2-diol itself does not undergo any thermal reaction. – ron Apr 18 '15 at 4:11

Compounds containing a cyclohexane-1,2-diol structure can undergo pinacol-like rearrangements. Usually, the substituent that is anti to the leaving group is the one that undergoes migration. Therefore, cis-cyclohexane-1,2-diol mainly yields cyclohexanone, whereas a trans-cyclohexane-1,2-diol mainyl yields cyclopentanecarbaldehyde.

• Can you please elaborate the answer with a figure? – Binary Geek Apr 18 '15 at 18:23
• But isn't the pinacol rearrangement an acid-catalyzed rearrangement, not a thermal rearrangement? The OP didn't mention acid, just heating. – ron Apr 18 '15 at 18:31