What's the R stand for?

[Bio-Hazard]

[NeonBlack]

The R can be pretty much anything.

[ecoli]

right... the "R" denotes any group of atoms. This is done to show whats "important" or the functional groups in the molecule.

[Yggdrasil]

The R represents the side chain of the amino acids which make up the anti-parallel beta sheet. Since a wide variety of side chains can exist on a beta -sheet, they generalize the structure by writing Rs instead of specific amino acid side chains.

 

In general, an R is an abbreviation in a chemical structure showing that something else goes where the R is, but the authors are too lazy to show the rest of the molecule, or the R-group is variable.

[RyanJ]

And I would alo like to add that there are a hell of a lot of them, here are a few links that may be of interest to you

 

http://sosnick.uchicago.edu/amino_acids.html

http://en.wikipedia.org/wiki/Amino_acids

 

Cheers,

 

Ryan Jones

[YT2095]

IIRC, R stands for Radical.

[donkey]

I don't think it does stand for radical. Side chains are not radicals!!

 

Here it is just the side chain of an amino acid (for example, the side chain of Glycine is just H and for alanine it is CH3).

 

I always took R groups in organic chemistry to be an organic group (where R sort of stood for rest [of the molecule])

[RyanJ]

I don't think it does stand for radical. Side chains are not radicals!!

 

Here it is just the side chain of an amino acid (for example' date=' the side chain of Glycine is just H and for alanine it is CH3).

 

I always took R groups in organic chemistry to be an organic group (where R sort of stood for rest [of the molecule'])

 

Or it could mean Replace as in this R should be replaced by something. thats the way out Biol. teacher explained it anyway

 

Cheers,

 

Ryan Jones

[X facter]

I thought R stood for Random.

[RyanJ]

I thought R stood for Random.

 

That would be a bit of a bad description I thibnk because amino acids and other organic cdompounds that involve an R group are not random they are infact highly organised and precise (Proteins coltroled through your [acr=Deoxyriboneucleic Acid]DNA[/acr]).

 

Cheers,

 

Ryan Jones

[YT2095]

I don't think it does stand for radical. Side chains are not radicals!!

 

Here it is just the side chain of an amino acid (for example' date=' the side chain of Glycine is just H and for alanine it is CH3).

 

I always took R groups in organic chemistry to be an organic group (where R sort of stood for rest [of the molecule'])

 

this would seem to sugest otherwise: http://www.wordreference.com/definition/methyl%20radical

 

I used Methyl as an arbitrary `R`

 

if we just look at the definition of Radical as used in chemistry: http://www.wordreference.com/definition/radical

 

it seems to be the exact function of the R in these molecules

[Skye]

R is one of the abbreviations used in organic chemistry for substituents. It refers to any alkyl substituent. Other commonly used abbreviations are Me for methyl, Et for ethyl, Ac for acetyl, Ph for phenyl, M for a metal and X for a halide.

 

For amino acids the R group generally means one of the standard amino acid side chains.

 

Radicals are often written with dots representing the electron, sort of like a Lewis diagram. Eg.

 

http://www.chemguide.co.uk/mechanisms/freerad/alkenehbr.html

[YT2095]

aren`t the one with the dots the Free Radicals? what happens in RCOOH for a carboxylic radical?

 

"Organic acids have hydrogen bonding and a carbonyl that gives them a double dose of polarity. The functional group is represented by a carbon, two oxygen atoms, and hydrogen. The general formula is R-C-O-O-H. One radical is attached to the carbon of the functional group."

 

since the Functional group here is the COOH, the R must be the Radical spoken of?

 

taken from :http://cms.firehouse.com/content/article/article.jsp?sectionId=18&id=18773

[Skye]

Yeah that is strange, I found this which says it explicitly. When I say strange, I mean I've never heard it used in that way. It might be the origin of the letter R, I don't know. Maybe some people just got it mixed up. Maybe it's just old fashioned, and not used any more to prevent confusion with 'free' radicals (which are often simply called radicals). In any case, whether you say 'R group' or 'radical' or whatever you like, it means an alkyl group (and H to be accurate). You can see from the examples, such as acetic acid (CH3COOH) where the R group would be CH3.

[YT2095]

I recon it is pretty old, I have chem text books here from the early 1900`s and they use it too.

 

I guess the REAL meaning isn`t all that important outside this particular question anyway, r could just as well mean Replacable for alot of it anyway

obviously in the case of the pic in the OP, an Amino acid looks like it should be there for the `R`, although I don`t know what the molecule is, it does look remakably DNA(ish) or at least Bio something or other.

I`m no expert in this area so the prior statement is ONLY suposition on my part

[Bluenoise]

I'm not sure why they call the R part of those carboxylic acid examples a "Radical", it's just an alkyl group.

A possibility maybe that they consider it a radical since the carbon is donating only one electron to the bond from it's valence shell and that the R group is only donating one as well. So if you treat them seperatley only posessing the electron that is originally theirs, I guess you could refer to them as radicals.

But it's a stretch and is pretty misleading.

 

Letting R stand for "Rest" makes a hell of alot more sense. Since that is how it's used.

 

And yeah that OP structure represents a hydrogen bonding formation found in a type of protein secondary structure called an "Anti-paralle Beta sheet", with the R groups represesnting amino acid side chain.

[YT2095]

I asked a good friend of mine today (a Chem proffesor) and the letter "R" does indeed stand for Radical and has done for some time, the Punctuation Has altered during that time though, and in the case of Benzene and the likes "AR" was used to indicate Aromatic Radical, the Dot for Free Radical and so forth

 

so yeah, "R" does indeed mean/stand for Radical.

 

this info also cost me a Beer afterwards!

[donkey]

Thanks, I appreciate you using your beer money to help educate us all

[Biology Tom]

My understanding is that it stands for "residue".

[zapatos]

You need some serious smelling salts and a heater to dig up something this old.