Can You Leave Out the 1's When Naming Organic Compounds?

[gsingh2011]

I have a few questions about organic chemistry. First of all, when is it acceptable to leave out the 1's when naming compounds? I've read that it's ok to leave out the 1 for something like bromobutane, as everyone will assume its on the first carbon. What about dibromobutane? Is it still acceptable to leave it out? What about 1-chloro-1-fluorobutane? Is it acceptable to write chloro-1-fluorobutane or chlorofluorobutane? Or if there's another functional group, like 1,2,2-tribromobutene, will the omission of the 1 before the butene still mean there is a double bond on the first carbon?

How do you name ethers and esters with substituents? They have two carbon chains, so I don't know how to name them when they have substituents on both chains. I couldn't find any examples online either...

One question on my homework from a while ago asked me to draw two different esters and state which was more polar than the other. Since the alkyl groups on both chains are nonpolar, and both esters obviously contain the same functional group, how can you have an ester that is more polar than another?

What is a dimer? In my notes it states that carboxylic acids often form dimers..

 

[Yanick]

As far as I know, you cannot omit numbers unless there is nowhere else that the substituent can be. For example, isopropyl alcohol does not need to be named propan-2-ol (that may be a bad example). Another one may be CH3CH2OH. You don't have to say ethan-1-ol because there are only two carbons and a hydroxyl group therefore there is no ambiguity when drawing the structure, you draw 2 carbons and put the -OH on either one and you will have ethanol. For things with 3+ carbons you start having ambiguity such as if I told you to draw propanol. It could be propan-1-ol or it could be isopropyl alcohol (which is propan-2-ol) for instance. You example for butane is, I think, the same. The tribromobutane is an example where you cannot have a double bond on any carbons except 3-4 because you will violate the octet putting a double bond anywhere else therefore you can omit the number representing the position of the double bond and still I will be able to draw the correct structure. You do read about traditional names in books and such but from what I know and have been taught it is not a true IUPAC name if the substituent is not numbered to tell one which carbon it is bonded to (assuming it can be drawn in more than one place and retain the name of course). In my limited experience I have learned that in order for a name to be appropriate someone who has never seen the molecule must be able to draw the proper structure/isomer etc just by reading the name. IMO the rest of the rules are a bit silly (like alphabetizing the substituents, lowest numbers etc, I personally think it would be much more logical to make the convention go from left to right of the parent chain then you can just go through the name and draw the molecule as you read it instead of having to jump around and count carbons 20 times).

Also when reading things written by chemists you will undoubtedly come upon names that violate many of the rules you have been taught because many compounds just have traditional names that chemists are so used to using that it is understood amongst them what is meant. It gets dicey when you are trying to learn the stuff as a student but it gets better with time and practice (I'm no expert and still a student mind you, but working in a BioChem lab I have noticed the difference by being exposed to real Chemists on a daily basis of my usage of the language), as with anything there is a learning curve that you must get through to learn the everyday language. I have, for example, taken 6+ years of Spanish in school and when I try and speak to many native speakers they laugh and tell me I say things wrong when in fact I am saying them correctly but everyday usage is not always the correct grammatical usage etc.

I'm not sure about complicated ethers/esters because I honestly can't think of something I've come across yet that has been much more complicated than diethyl ether and what not. I'm sure you'll get an answer to that question from someone else.

As far as dimers go, they are the joining of two monomers. Three are called trimers but more often than not more than two are just called polymers. Helpful? Probably not. A monomer is any type of unit which can be bonded to another type of unit which is either similar to or exactly the same as the original. For example, amino acids are monomers and can be linked to form dimers, trimers etc. Amino acid polymers are called proteins. Polyvinyl Chloride (CH2CHCl)n is a polymer of vinyl chloride (CH2CHCl), the latter is the monomer. When two are linked you can call them a dimer, 3 can be called trimer and you can probably extend this thinking to call 4 tetramers, 5 pentamers etc but from what I have seen you just call more than 2-3 a polymer. The term monomer does not mean anyone specific molecule just a unit which can be bonded to similar or equivalent units to make a chain. Proteins/Amino acids, Sugars(or polysaccharides)/monosaccharides, Polyvinyl Chloride/Vinyl Chloride, DNA/nucleotides are all polymer-monomer type pairs, and they are not the only ones by far.

Hope this helps!

 

[chemisttree]

How do you name ethers and esters with substituents? They have two carbon chains, so I don't know how to name them when they have substituents on both chains. I couldn't find any examples online either...

Use something like methyl ethyl ether as a guide. For ethers, name one substituent then the other followed by the word 'ether'. IUPAC nomenclature uses a http://old.iupac.org/reports/provisional/abstract04/favre_310305.html" Complicated ethers might not even be named as such. For example, an ether of isopropane and methyl (methyl isopropyl ether) is named 2-methoxypropane. It is named as a (methoxy) derivative of an alkane.

One question on my homework from a while ago asked me to draw two different esters and state which was more polar than the other. Since the alkyl groups on both chains are nonpolar, and both esters obviously contain the same functional group, how can you have an ester that is more polar than another?

Bulkier or longer nonpolar tails will make the whole molecule less polar.

What is a dimer? In my notes it states that carboxylic acids often form dimers..

You can form a dimer with your hands and fingers. To model a carboxylic acid dimer, place your right index finger on your left thumb and your left index finger on your right thumb. In this case the thumb is the carbonyl oxygen and the finger is the acidic -OH group.