My previous dissection of the mechanism for ester hydrolysis dealt with the acyl-oxygen cleavage route (red bond). There is a much rarer[cite]10.1039/jr9550001522[/cite] alternative: alkyl-oxygen cleavage (green bond) which I now place under the microscope.
Posts Tagged ‘energy’
The mechanism of ester hydrolysis via alkyl oxygen cleavage under a quantum microscope
Tuesday, April 2nd, 2013A sideways look at the mechanism of ester hydrolysis.
Friday, March 29th, 2013The mechanism of ester hydrolysis is a staple of examination questions in organic chemistry. To get a good grade, one might have to reproduce something like the below. Here, I subject that answer to a reality check.
Understanding the electrophilic aromatic substitution of indole.
Sunday, March 3rd, 2013The electrophilic substitution of indoles is a staple of any course on organic chemistry. Indoles also hold a soft-spot for me, since I synthesized not a few as part of my Ph.D. studies.[cite]10.1039/P29750001209[/cite],[cite]10.1039/P29770000281[/cite] The preference for substitution in the 3-position is normally explained using the arrows shown below (position 3=green,2=blue,1=red). Here I explore how these arrows might be interpreted in terms of various quantum mechanical properties.
A to-and-fro of electrons operating in s-cis esters.
Thursday, February 21st, 2013The conformational preference of s-cis amides.
Sunday, February 10th, 2013Amides with an H-N group are a component of the peptide linkage (O=C-NH). Here I ask what the conformation (it could also be called a configuration) about the C-N bond is. A search of the following type can be defined:
The conformation of acetaldehyde: a simple molecule, a complex explanation?
Friday, February 8th, 2013Consider acetaldehyde (ethanal for progressive nomenclaturists). What conformation does it adopt, and why? This question was posed of me by a student at the end of a recent lecture of mine. Surely, an easy answer to give? Read on …
How does one describe the wavefunction for the π-complex formed from PhNHOPh?
Friday, January 25th, 2013Although have dealt with the π-complex formed by protonation of PhNHOPh in several posts, there was one aspect that I had not really answered; what is the most appropriate description of its electronic nature? Here I do not so much provide an answer, as try to show how difficult getting an accurate answer might be.
The π-complex in the benzidine rearrangement: a molecular orbital analysis.
Friday, January 18th, 2013Michael Dewar[cite]10.1016/S0040-4039(01)82765-9[/cite] famously implicated a so-called π-complex in the benzidine rearrangement, back in the days when quantum mechanical calculations could not yet provide a quantitatively accurate reality check. Because this π-complex actually remains a relatively unusual species to encounter in day-to-day chemistry, I thought I would try to show in a simple way how it forms.
Hydrogen bond strength as a function of ring size.
Thursday, January 3rd, 2013One frequently has to confront the question: will a hydrogen bond form between a suitable donor (lone pair or π) and an acceptor? One of the factors to be taken into consideration for hydrogen bonds which are part of a cycle is the ring size. Here I explore one way of quantifying the effect for the series below, n=1-5 (4-8 membered rings).