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Topic: IUPAC: double bond interpretation?  (Read 572 times)

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Offline Kaspijs

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IUPAC: double bond interpretation?
« on: January 29, 2020, 11:26:35 AM »
According to some sources according to IUPAC a double bond has a higher priority than a single bond. However, some others state that a double bond can be interpreted as two single bonds leading to two of the elements further in chain, unattached to any other. Thus, depending on which principle is used the R/S configuration varies, for example, 2-chloro-3,3-dihydroxypropanal (attached).

So which is the correct one and why is?

Unfortunately I do not reckon the sources, yet Wikipedia proposes the first method and second comes from some sort of Russian org chem book.

Offline hollytara

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Re: IUPAC: double bond interpretation?
« Reply #1 on: January 29, 2020, 11:38:32 AM »
A double bond is counted "backward and forward" by being turned into virtual single bonds.

So an aldehyde group has a C connected to two O's and an H, then an O connected to two C's

The germinal diol or aldehyde hydroate you show has a C connected to two O's and an H, but each O is connected to only one C and one H. 

Since the second bond to C is to a higher atomic number atom than to an H, the aldehyde group has higher priority.

If you look up the book by Jakob Fredlos, it is all explained very simply.

Offline chenbeier

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Re: IUPAC: double bond interpretation?
« Reply #2 on: January 29, 2020, 11:48:37 AM »
Die Name is wrong, Check Red an black coloured Bonds.


It has two Hydroxymethyl Groups HO-CH2- instead of Hydroxy- group.

2- chloro- 3- hydroxymethyl - 4- hydroxy- butanal

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