How to use regexp to identify the number of hydrogens in a chemical formula?

Question

Which expression should I use to identify the number of hydrogen atoms in a chemical formula?

For example:

C40H51N11O19 - 51 hydrogens

C2HO - 1 hydrogen

CO2 - no hydrogens (empty)

Any suggestions?

Thanks!

Cheers!

You will need more than just a regular expression to do this, what language are you using ? — M0nst3R, Sep 26 '17 at 13:10
Whatever answer you accept, check the result for something with mercury. — Yunnosch, Sep 26 '17 at 13:32
Better add some sample input with mercury and maybe multiple groups containing H, like ethyl ether. Otherwise your question is unclear/too broad and will get probably ultimatly unsatisfying answers which at first seem adequate. — Yunnosch, Sep 26 '17 at 13:37
thanks for your observation @Yunnosch . However, I'm working only with biomolecules — German Andres Preciat Gonzalez, Sep 26 '17 at 13:51

Conner · Answer 1 · 2017-09-26T13:21:27.907

0

A Regex Expression that will match H with follwowing digits would be:

/H(\d+)/g

The 'H' is a literal charecter match to the H in the given chemical formula
() declares a capture group, so you cna then grab the captured group without the H in whatever programming language you are using
\d will match any digit along with the + modifier that matches 1 or more

There is no catch all scenarios here, you might be best using something other than a regex.

edited Sep 26 '17 at 13:21

answered Sep 26 '17 at 13:16

Conner

There is no catch all, I agree; but this does not even get all the cases OP gave as sample input. E.g. "C2HO" – Yunnosch Sep 26 '17 at 13:18
@Yunnosch I agree completely, which is why I suggested using somethying else, however I have added this as an answer for the OP to start off with, maybe give them some guidance on regex. – Conner Sep 26 '17 at 13:20
Then maybe something like `([A-Z][a-z]*)(\d+*)` to take into account both digits and element names. – Conner Sep 26 '17 at 13:33

score 0 · Accepted Answer · answered Sep 26 '17 at 13:18

0

You can start using this regex :

H\d*

H -> match literaly the H caracter d* -> match 0 to N time a digit

see exemple and try yourself other regex at : https://regex101.com/r/vdvH8S/2

But regex wont convert for you the result, regex only do lookup.

You need to process your result saying :

answered Sep 26 '17 at 13:18

baddger964

2 Answers2