Modification of Phenethylamines and Differences on the Benzene Ring???

[d-Dexter-25]

On the benzene ring of the Phenthylamine there are numbered substitution points like the 4 position ans so forth. Well when I look at pictures on either erowid or somewhere else I notice something really strange, MDMA has the 3,4 position backwards from the positions as they appear on other Phenethylamines like say 2C-B which is substitued at the 2,4,5 positions and MDMA at the 3,4 positions. I understand where to start from when counting and even if I did'nt its backwards!!!

I'm sure there must be a good reason for this that more experienced persons can explain to me. Its very wierd though why would'nt it be uniform for all Phenthylamines substituted in that manner???

 

[vecktor]

its simple, the ring carbon attached to the ethylamine is numbered 1, then you count either way round to get the smallest numbers, so 6-methoxy phenethylamine would be called 1-methoxy phenethylamine. and so on
v

 

[d-Dexter-25]

I'm a idiot in case you saw my first responce which was stupid but why don't they just go one way why do it so what ever substituted position is the first to reach starts the numbering in that direction??? Well actually it does make some sense so I guess I can see it!!!

 

[d-Dexter-25]

Ok I think I understand and I thought Vecktor you were trying to state how the ring is numbered as if I did'nt know like 1-6 but I just disregarded your message as being for someone who did'nt know anything which I don't know much but why do they do it like this????

 

[MurphyClox]

its simple, the ring carbon attached to the ethylamine is numbered 1, then you count either way round to get the smallest numbers, so 6-methoxy phenethylamine would be called 1-methoxy phenethylamine. and so on
v

Small mistake here: Position 6 (ortho) equals position 2 (ortho, too!) not 1, if there are no other substituents.
Position 1 is, as Vecktor elaborated correct, the position which connects to the alkyl sidechain.

- Murphy

 

[Doctor Abalaba]

Im a lay chemist (pick up what I can mainly from reading you guys).
Could someone put up a pic, labeling the positions. I had the exact same question.

 

[MurphyClox]

The reason why the one compound is numbered clockwise while the other is counter-clockwise was explained by Vecktor:

then you count either way round to get the smallest numbers

YO! Murphy

 

[Bob Loblaw]

Any particular reason for the smallest numbers?

 

[MurphyClox]

Any particular reason for the smallest numbers?

It's just one of the basic rules in nomenclature of organic compounds, established by the Union for Pure and Applied Chemistry (IUPAC). A nice summary can be found here.

If you look for example at 2C-B, one could name it 4-bromo-2,5-dimethoxyphenethylamine (like in the pic above) or 4-bromo-3,6-dimethoxyphenethylamine (when numbering the other way around). To avoid unnecessary confusion, the abovementioned rule was established.

Peace! Murphy

 

[Bob Loblaw]

Thanks ^_^