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According to IUPAC, a hemiacetal is a compound having the general formula $\ce{R2C(OH)OR'}$ $\ce{( R' ≠ H )}$.

What does the order in which the elements of this formula appear tell us about the connectivity of this molecule? Does it tell us anything besides that a compound with this formula is composed of a carbon, a hydroxyl group, a oxygen, a $\ce{R2}$ group and a $\ce{R'}$ group? Or does it contain any information about how these elements and groups are connected with each other, about the compound's structure?

Surely the order in which these elements appear isn't arbitrary.

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  • $\begingroup$ The formula tells you that the two R groups are bonded to carbon as are OH and OR'. The (OH) is written that way so you don't see R2COHOR and possibly misinterpret the formula. $\endgroup$ – user55119 Nov 26 '17 at 18:31
  • $\begingroup$ @user55119 Is there any reason why it's $\ce{(OH)OR'}$ and not $\ce{(OR')OH}$? $\endgroup$ – Qwedfsf Nov 26 '17 at 18:54
  • $\begingroup$ I don't see why not. Perhaps there is a rule. Clarity is important. $\endgroup$ – user55119 Nov 26 '17 at 18:59
  • $\begingroup$ Related: What is the meaning of parentheses in a condensed molecular formula? $\endgroup$ – Loong Nov 27 '17 at 6:34
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These molecular formulas have a very limited amount of information which they can give us. As far as I know, there is no order of bonding nor explanation in how for example this hemiacetal is really structured. They are merely created for you to maybe identify such a group if needed one day (lets say in a bigger molecule). And why its probably (OH)OR`and not the other way around is because of the alphabetical order (H before R). My advice: Don't rely on them, they can be used in a number of ways and have, for my knowledge, no fixed usage. In the golden book of IUPAC it even says "Compounds having the general formula..." meaning that yes, this formula generally applies on hemiacetals, but not always.

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