The Randic index: 40 years and counting

I have been meeting with some undergraduate students who are keen to do research over the Summer. While answering their questions, I kept coming back to how I myself was drawn to research many years ago. As I found rocket science boring, I eventually stumbled upon chemistry, which really captivated my attention. But you might ask me: what was it that got you interested in organic chemistry back in 1988 (this is when I just started my second year of undergrad in Moscow). I was trying to recall the first paper I had read that really made me think more about organic chemistry. In fact, I now remember that paper quite well. It was the 1975 account by Randic in JACS (given to me by my advisor, V. Palyulin). In it, Randic introduced a mathematical index that later became associated with his name. The most fascinating thing about this parameter is that it looks at molecules as if they were “graphs”. Below is how this index is calculated. There are several molecular properties that show a linear correlation with the Randic index. I think there is something magical in correlating a measurable physical property with something that has nothing to do with any advanced quantum mechanics, but is merely a reduction of a chemical structure to a number. This seems really bizarre. Underneath the formula you see how a correlation with boiling points in a hydrocarbon series would look like (but please look at the JACS paper for the “real” thing, I just reproduced what I saw there using ChemDraw). For me, this is pretty interesting (and I still do not fully understand this stuff).


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