A game chemists often play is to guess the mechanism for any given reaction. I thought I would give it a go for the decomposition of the tris-peroxide shown below.
Thalidomide is a chiral molecule, which was sold in the 1960s as a sedative in its (S,R)-racemic form. The tragedy was that the (S)-isomer was tetragenic, and only the (R) enantiomer acts as a sedative. What was not appreciated at the time is that interconversion of the (S)- and (R) forms takes place quite quickly in aqueous media.
The text books say that cyclohexenone A will react with a Grignard reagent by delivery of an alkyl (anion) to the carbon of the carbonyl ( 1,2-addition ) but if dimethyl lithium cuprate is used, a conjugate 1,4-addition proceeds, to give the product B shown below.
When methyl manganese pentacarbonyl is treated with carbon monoxide in e.g. di-n-butyl ether, acetyl manganese pentacarbonyl is formed. This classic experiment conducted by Cotton (of quadruple bond fame) and Calderazzo in 1962[cite]10.1021/ic50001a008[/cite] dates from an era when chemists conducted extensive kinetic analyses to back up any mechanistic speculations. Their suggested transition state is outlined below.
Following on from our first mechanistic reality check, we now need to verify how product A might arise in the mechanism shown below, starting from B . This pathway backtracks the original one in reversing the final arrow of that process (shown in red in previous post and in magenta here for the arrow in reverse), to go uphill in energy to reach the secondary (unstabilised) carbocation.
The reaction described in the previous post (below) is an unusual example of nucleophilic attack at an sp 2 -carbon centre, reportedly resulting in inversion of configuration[cite]10.1021/ja00765a062[/cite]. One can break it down to a sequence of up to eight individual steps, which makes teaching it far easier. But how real is that sequence?
The reaction below plays a special role in my career. As a newly appointed researcher (way back now), I was asked to take tutorial groups for organic chemistry as part of my duties. I sat down to devise a suitable challenge for the group, and came upon the following reaction[cite]10.1021/ja00765a062[/cite]. I wrote it down on page 2 of my tutorial book, which I still have.
Every once in a while, one encounters a molecule which instantly makes an interesting point.
I occasionally delve into the past I try to understand how we got to our present understanding of chemistry.
There is often a disconnect between how a text-book (schematically) represents a reaction and a more quantitive “reality” revealed by quantum mechanics. Is the bromination of ethene to give 1,2-dibromoethane one such example? Text-books will show how ethene interacts with bromine to form a cyclic bromonium cation, which with the liberated bromide anion makes for an ion-pair.
The conformational analysis of cyclohexane is a mainstay of organic chemistry. Is there anything new that can be said about it? Let us start with the diagram below: This identifies the start of the process as a chair conformation of cyclohexane, with D 3d symmetry.
