March 29, 2024, 07:52:00 AM
Forum Rules: Read This Before Posting


Topic: Why write H2C not CH2?  (Read 3457 times)

0 Members and 1 Guest are viewing this topic.

Offline Miriiii

  • Very New Member
  • *
  • Posts: 1
  • Mole Snacks: +0/-0
Why write H2C not CH2?
« on: April 29, 2019, 08:41:22 AM »
So I stupidly enrolled in biochemistry this semester despite having not been in a chemistry class since I was 15. I have a lot of basic questions.

I am trying to memorise the structure of proline. Noticed that its side chain is 3 CH2 groups. 2 Are CH2, one is H2C, what's the difference. Why would you write them differently?

Similarly, I've noticed that NH2 groups are written as H2N a lot of the time, why? When do you flip this around?

Cheers! And respect to you chem people, trying to wrap my head around this is doing me in.

Offline chenbeier

  • Sr. Member
  • *****
  • Posts: 1348
  • Mole Snacks: +102/-22
  • Gender: Male
Re: Why write H2C not CH2?
« Reply #1 on: April 29, 2019, 09:40:47 AM »
You have a molecule H2N-R-X  another one is Y-R-NH2. At least it doesnt matter how you write it.
Or you have H2C=CH2 which show the doublebond between the carbon atoms. It is not wrong to write CH2CH2.

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27634
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Why write H2C not CH2?
« Reply #2 on: April 29, 2019, 09:48:41 AM »
These are the same things, just seen from different sides.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline Corribus

  • Chemist
  • Sr. Member
  • *
  • Posts: 3471
  • Mole Snacks: +526/-23
  • Gender: Male
  • A lover of spectroscopy and chocolate.
Re: Why write H2C not CH2?
« Reply #3 on: April 29, 2019, 11:13:36 AM »
If you wrote CH2=O for, e.g., formaldehyde, it could be mistaken which nucleus is attached to the oxygen. With H2C=O, it is unambiguous that the carbon is attached to the oxygen. Likewise for O=CH2. This is really most important when you are drawing bonds.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

Sponsored Links