In my previous post I speculated why bis(trifluoromethyl) ketone tends to fully form a hydrate when dissolved in water, but acetone does not. Here I turn to asking why formaldehyde is also 80% converted to methanediol in water? Could it be that again, the diol is somehow preferentially stabilised compared to the carbonyl precursor and if so, why?
Posts Tagged ‘Tutorial material’
Spotting the unexpected. The hydration of formaldehyde.
Monday, March 12th, 2012Spotting the unexpected. The trifluoromeric effect in the hydration of the carbonyl group.
Friday, March 9th, 2012The equilibrium for the hydration of a ketone to form a gem-diol hydrate is known to be highly sensitive to substituents. Consider the two equilibria:
The hydroboration-oxidation mechanism: An updated look.
Sunday, February 26th, 2012One thing almost always leads to another in chemistry. In the last post, I described how an antiperiplanar migration could compete with an antiperiplanar elimination. This leads to the hydroboration-oxidation mechanism, the discovery of which resulted in Herbert C. Brown (at least in part) being awarded the Nobel prize in 1979. (more…)
E2 elimination vs ring contraction: anti-periplanarity in action.
Monday, February 20th, 2012The anti-periplanar principle permeates organic reactivity. Here I pick up on an example of the antiperiplanar E2 elimination (below, blue) by comparing it to a competing reaction involving a [1,2] antiperiplanar migration (red). (more…)
An exothermic E2 elimination: an unusual intrinsic reaction coordinate.
Monday, February 6th, 2012The previous post explored why E2 elimination reactions occur with an antiperiplanar geometry for the transition state. Here I have tweaked the initial reactant to make the overall reaction exothermic rather than endothermic as it was before. The change is startling.
An orbital analysis of the stereochemistry of the E2 elimination reaction
Saturday, February 4th, 2012The so-called E2 elimination mechanism is another one of those mainstays of organic chemistry. It is important because it introduces the principle that anti-periplanarity of the reacting atoms is favoured over other orientations such as the syn-periplanar form; Barton used this principle to great effect in developing the theory of conformational analysis. Here I explore its origins. (more…)
Secrets of a university tutor: dissection of a reaction mechanism. Part 2, the stereochemistry.
Monday, January 30th, 2012In the previous post, I went over how a reaction can be stripped down to basic components. That exercise was essentially a flat one in two dimensions, establishing only what connections between atoms are made or broken. Here we look at the three dimensional arrangements. It all boils down to identifying what the stereochemistry of the bonds marked with a wavy line are. (more…)
Secrets of a university tutor: dissection of a reaction mechanism.
Wednesday, January 25th, 2012Its a bit like a jigsaw puzzle in reverse, finding out to disassemble a chemical reaction into the pieces it is made from, and learning the rules that such reaction jigsaws follow. The following takes about 45-50 minutes to follow through with a group of students.
Shared space (in science).
Friday, January 6th, 2012I thought I would launch the 2012 edition of this blog by writing about shared space. If you have not come across it before, it is (to quote Wikipedia), “an urban design concept aimed at integrated use of public spaces.” The BBC here in the UK ran a feature on it recently, and prominent in examples of shared space in the UK was Exhibition Road. I note this here on the blog since it is about 100m from my office.
Molecular gymnastics in 2+2 cycloadditions. Two different moves compared.
Thursday, December 15th, 2011The previous post showed how the 2+2 cycloaddition of an alkene could occur by a sort of sideways insinuation of the bonds. I have also shown how the same reaction can occur with a dramatic rotation of one of the double bonds. This post compares the two moves side by side.