How to read a molecule

[QUARE]

So my question is how do I get the name of a molecule simply by looking at it ?

First question: how do I know that are the position on exemple; a Phenyl ring
Where is position; 1, 2, 3, 4, 5 ,6

Exemple: Dopamine name is 3,4-dihydroxyphenethylamine
So dihydroxy is on position 3 and 4 but which one is which
and on which position is the ethylamine tail

Now getting a little more complicated
A Benzodiazepine exemple; Lorazepam, its name is
(RS)-9-chloro-6-(2-chlorophenyl)-4-hydroxy-2,5-diazabicyclo[5.4.0]undeca-5,8,10,12-tetraen-3-one

What mean the (RS)
the name start with 9-chloro, is that the bottom on the molecule or the left side and why do we start there
6-(2-chlorophenyl) I think is the bottom
4-hydroxy is clearly the right side of the big ring
what is the name of that big ring
I have no idea what the rest of the name mean, what is what and why is it in that order

More clearly my question is: Where do we start, what are the position on a ring or any other place on a molecule and also could anyone link me to a site or something that could teach me the name of most structure.

Im sorry if my question is not clear, I dont know much about how to find the name simply by looking at the molecule and I would really like to know how

Thanks a lot

 

[adams49]

QUARE, the big ring is a benzene ring. The number sequence starts at 4oclock position unless connecter to a benzene ring. I could fill this forum up with trying to teach this over this media so get an organic chemistry book. It don't matter how old because the (nomenclature) which means name in chemistry has not changed. The first chapter will be on the positions of functional groups like CH3 OH NO2 ect. The numbers will respond to a name also according to position so u will see trans, cis, oxy, butyl ect. I hope this gives u a start. Go to a organic chemistry nomenclature site along with the book and you will figure it out. It will take a litttle time if u have no prior chemistry knowledge. Good Luck
adams49

 

[alovesupreme]

oooh man you just need to find a good orgo textbook at your local used bookstore and all will be revealed. but let me try to help a bit to whet your whistle... i can be a bit rusty but the best way to stay sharp is to teach others...

(1) the numbering on the phenyl ring is relative to the major substituent, R. let me introduce a few new terms:

ortho: two substituents are "ortho" to one another if they are on adjacent carbons on the phenyl ring
meta: two substituents are "meta" to one another if they are separated by one carbon on the phenyl ring
para: two substituents are "para" to one another if they are separated by two carbons on the phenyl ring

so in your diagram above, the "ethylamine" substituent is position 1, the "meta" hydroxyl group (upper left) is position 3 and the "para" hydroxyl group (lower left) is position 4.

as adams notes, when you have multiple substituents, there is a certain order of rules that you use to determine the "dominant" substituent which you consider position 1, then work from there.

(2) more complicated example. the (R,S) refers to the fact that this molecule has two stereocenters and you are referring to one particular of four possible optical isomers. this is a little bit more advanced topic in chemical structure. simply put think of it as that the substituents at stereocenters can be arranged in various orders and this ultimately can affect molecular conformation and thus chemical/pharmacological activity...

we didn't really discuss deriving names for compounds this complex from scratch in the orgo classes i had the opportunity to take... so don't feel too bad about it, lol. even the pros use software these days to get a proper IUPAC name for a complex compound. focus at first more on being able to accurately match up substituents and positions in the name to positions in a diagram of the structure.

the big ring is called a "diazepine ring". the fused phenyl ring to the left of the "diazepine" is what makes the pictured molecule a "benzo"-"diazepine".

have fun!

 

[sekio]

This is the IUPAC naming system, there are plenty of resources on it out there.

Here's a good tutorial, and here's a comprehensive guide to the naming terms. If you want a little more comprehensive knoledge, find a first year organic chemistry textbook online and read it.

 

[QUARE]

Thanks a lot! I have some reading to do now.

 

[Hammilton]

Yeah, biochemdraw3d is a huge asset in getting accurate names. It's not perfect, especially with complicated multicyclic groups but it's better than nothing.

Here's something that tricked me for a long time: compounds that are considered bi, tri, tetra or whatever refers only to the fused ring system. Adding a phenyl substitution to a tri cyclic structure still leaves you with a tri cyclic structure. It's only when you fuse a benzene ring to that structure so you upgrade. Not actually relevant to naming so much but useful in conversation.

 

[alovesupreme]

let me give you a book recommendation; i have read many orgo texts modern and historic (i have a little collection) and i feel the best one of them all is titled "organic chemistry structure and reactivity" by seyhan ege. try to get at least a third edition. you should be able to find one on ebay, amazon, abebooks, whatever and have it shipped right to your door for $10-20. professor ege was a brilliant writer and broke down orgo for the reader like nobody else could. another fave is "organic chemistry a short course" by hart and schuetz, this is an older book and does not have the scope and depth of ege's text but it's a nice quick read and a good primer. enjoy your studies!

edit: i see the short course has continued to have been updated and published and is currently in an 11th printing. that's cool. there may be a bit more depth to it versus my first or second printing (i'd have to look) but i'm not sure.