# How does spin flipping of triplet carbenes occur?

Below is presented a page from Clayden Organic Chemistry 2ed.

How and why does the spin flipping during the collision with solvent molecules actually occur?

• "How" does not have a proper answer as in quantum physics there is no good way to describe interaction of two systems, but only one system. And for one system the question has no answer. "Why" does have an answer: it is because spin flip requires consumption/release of energy that must go to/from somewhere. – permeakra Apr 27 '16 at 19:30
• The same factors that relax forbidden singlet-triplet spectroscopic transitions apply here. See this earlier answer for some discussion of this topic. – ron Apr 27 '16 at 19:57
• Could you write an answer? – RBW May 1 '16 at 14:07

The triplet state corresponds to the three images on the left and the singlet to that on the right. If you look at the triplet with $m_s=0$ you will see that to convert it to a singlet all that is needed is a re-phasing of the spins from parallel to anti-parallel.
• also I forgot to mention that (a) heavy atoms in solvent, such as Xe gas, I$^-$ or as an iodo solvent will cause spin-orbit interaction. Chlorinated solvents will also do so but to a lesser extent. (b) The solvent also mediates the interaction reciprocally due to its dielectric constant, the larger this is the smaller the interaction. (c) As the carbene tumbles in solution it cuts through the earth's magnetic field, thus it effectively experiences a random field, this also will induce transitions. – porphyrin Jul 12 '16 at 14:42