# Chemical formula of ethanol and other carbon compounds

Should chemical formula of ethanol be written as $\ce{CH3CH2OH}$ or $\ce{C2H5OH}$? And whats the logic behind it? I have seen the former being used more often, so why is ethane represented by $\ce{C2H6}$ than $\ce{CH3CH3}$?

$\ce{CH3CH2OH}$, and $\ce{C2H5OH}$ or $\ce{EtOH}$ (Ethyl OH) tells you specifically what are the bonds in the molecule. $\ce{CH3H6O}$, which would be the equivalent of writing ethane like $\ce{C2H6}$, on the other hand, tells you nothing, since it can be both ethanol or dimethyl ether. Bigger formulas can represent thousends of different compounds if written like that.

The reason why $\ce{C2H6}$ is used instead of $\ce{CH3CH3}$ is because it can only represent ethane - it's a very simple compound with no isomers, so you can write it both ways.

You can write ethanol both ways you suggested, although I've never seen $\ce{C2H5}$ instead of $\ce{Et}$ anywhere but in examples. What you shouldn't do is write it like $\ce{C2H6O}$.

If you were asking what is the logic of $\ce{CH3CH2OH}$:

What it's telling you is that the compound it is representing [ethanol] consists of a carbon atom bonded to 3 hydrogen atoms and to another carbon atom, which is bonded to 2 hydrogen atoms and 1 oxygen atom, which is finally bonded to 1 hydrogen atom, as follows:

• Good. But didn't you mean ‘C₂H₆O' instead of ‘CH₃H₆O'(??) in the 1st paragraph, too? Oct 26 '18 at 21:28

I think that organic chemists tend do prefer $$\ce{CH3CH2OH}$$ (condensed) formula over $$\ce{C2H5OH}$$ (not mentioning favorite abbr. EtOH) because we/they like to see each carbon atom separated in the formula.*
$$\ce{C2H5OH}$$ looks like some ugly hybrid between molecular formula ($$\ce{C2H6O}$$) and nice condensed formula.

I speculate that most organic chemists are, for some reason, more comfortable with $$\ce{C6H5\bond{-}}$$ for phenyl (not speaking of $$\ce{Ph\bond{-}}$$) than $$\ce{C2H5\bond{-}}$$ for ethyl, even though it can mean multiple different structural isomers, e.g. $$\ce{HC#C-CH2-C#C-CH2\bond{-}}$$ (hexa-2,5-diyn-1-yl).

$$\ce{C2H5\bond{-}}$$ is unambiguous and represents only ethyl group. I think we should learn to be more comfortable with it.

*) In formulae like $$\ce{(CH3)3C\bond{-}}$$ (tert-butyl) or $$\ce{CH3[CH2]7\bond{-}}$$ (octyl), many carbons are not explicitly written (repeating units), but they are still written separately. No subscript index number $$\ce{C_x}$$ used.