Organic chem help

[HERculina]

1)How do you draw diethylamine? Is there two NH2 s on the first carbon or is it one NH2 for each carbon in the molecule?  2) Are both considered correct  or just one of these: 4-chloro-3-methyl-but-2-ene and 3-methyl-4-chloro-but-2-ene 3) Say you had a a 4 carbon unbranched chain with a methyl group on the 2nd Carbon and an ethyl group on the 3rd do you numberthe carbons from right to left or left to right? What would be the name? Thanks. 

[jasoN-]

1) amine: NH3
ethyl: R-CH2CH3
diethylamine: NH(CH2CH3)2

2) 4-chloro-3-methylbut-2-ene is the correct name (notice the subtleties, there's no space/hyphen between methyl and butene)

3) Well if you had those groups you mentioned, your parent chain would be pentane, with methyl groups on position 2 and 3, so the name would be 2,3-dimethylpentane
However I see what you're trying to ask, you would name from the ethyl side (right to left, i.e. higher priority first)
so 2-ethyl-3-methylbutane would be more correct than 2-methyl-3-ethylbutane
But of course, the actual correct name would be 2,3-dimethylpentane as I mentioned earlier.

EDIT: in regards to question 2), the correct name would in fact be 1-chloro-2-methylbut-2-ene
HOWEVER if the double bond were in position 1, then it would be 4-chloro-3-methylbut-1-ene

[Aurelian]

1)How do you draw diethylamine? Is there two NH2 s on the first carbon or is it one NH2 for each carbon in the molecule?

Diethylamine has one amino group with two ethyl groups - one either side of the amino groups. It is therefore a secondary amine. It has the semi-structural formula CH3CH2NHCH2CH3.

2) Are both considered correct  or just one of these: 4-chloro-3-methyl-but-2-ene and 3-methyl-4-chloro-but-2-ene

According to IUPAC rules, after assigning substituent numbers, you should list substituents alphabetically when constructing the final name. Thus, 4-chloro-3-methyl is 'correct', while 3-methyl-4-chloro is 'incorrect'. Not that prefixes such as "di", "tri" etc do not count in this alphabeticity. Thus, "tetrachloro" would still come before "ethyl", because c comes before e.

 3) Say you had a a 4 carbon unbranched chain with a methyl group on the 2nd Carbon and an ethyl group on the 3rd do you numberthe carbons from right to left or left to right? What would be the name?

Just go back to your basic principles; isolate the longest carbon chain, number the carbons left to right, and then right to left, and go with the one which yields the lowest number. In this case, I do not believe you have found the longest carbon chain if you are still considering there to be an ethyl group!

Comments in bold. Hope that helps!

[charmanderp]

1) Rather than two amino groups, you here have two ethyl groups! The 'di' refers to the ethyl. So you have an NH as your parent molecule, with a C2H5 on either side, taking the nitrogen atom's remaining bonding electrons.

You appear to have confused it with ethylenediamine aka 1,2-diaminoethane.

2) Neither of those is considered correct. You always want the lowest sum of numbers when numbering your substituents, and hence it should be 1-chloro,2-methylbut-2-ene.

3-methyl-4-chloro-but-2-ene - or indeed 2-methyl,1-chlorobut-2-ene - is undesirable as your prefixes should be ordered in alphabetical order. Thus 'chloro' comes before 'methyl', as c comes before m.

3) My understanding is that a carbon chain with attached methyl and ethyl groups would NOT be an 'unbranched chain'.

Regardless, your first step is to identify the longest carbon chain. That is indeed, a carbon chain with 5 carbons, so it is 'something' pentane. We have methyl groups attached to two different carbons, so as in question 2 we will contrive to get the lowest sum of numbers on our substituents. It will be either '3,4' or '2,3' - the latter is preferable, and hence we have 2,3-dimethylpentane.

[HERculina]

Ok thanks Guys 1) I thought that that structure would be called N-ethyl-1-ethylamine. And the book drew it like this: H2N -CH2-CH2-NH2 2) So if it was fluoro instead of chloro would u have the methyl first? You don't look at halogens being a higher priority than alkyls, but alhphabetically? And thanks for reminding me about where the hyphens should be 3) get this now 

[charmanderp]

2) Prefixes such as 'di' and 'tetra' only apply to a functional group or substituent if they come directly before it. For example, it's always 1,2-propandiol, rather than 1,2-dipropanol.

2) F comes before m, so fluoro would still be before methyl :p In terms of substituents, there is no order of precedence, that applies only to the main functional group.

Note that it is 1-chloro-2-methylbut-2-ene, rather than 4-chloro-3-methylbut-2-ene as you've suggested.

[HERculina]

O that's right. That would be because C-Cl has higher priority over C=C? Ahahah i clearly don't know my alphabet Ok so if it was fluoro and ethyl, ethyl would be before right? Oh i get that, plus ethyl isn't really a functional group. With the 1,2-propandiol thing does that molecule have two OHs in it?

[charmanderp]

No, C=C has higher priority over C-Cl, which never has priority. It's always chloroethane, never ethanechloro! The reason it is 1,2 rather than 4,3 is because you always want the lowest sum of numbers. 1+2=3 < 4+3=7

Indeed, ethyl would come before fluoro, given that the ethyl wasn't part of the longest carbon chain.

And yes, 1,2-propandiol has two hydroxy groups.

[HERculina]

Ohhh so there's a lowest sum rule. Is it this for every naming case?

[HERculina]

And i get what you mean with question one now. Like dichloromethane how theres two chlorine atoms and only one carbon i think my bookS answer accidentally had the strucure wrong as well.

[HERculina]

Hello again, which is the correct systematic name: 2,2,2-trichloro-1,1-ethandiol or 2,2,2-trichloroethane-1,1-diol ? If a question asks you to draw the structural formulae and you had OH or NH2 do u just write that and attach it with the carbon or should you write O-H or H-N-H on the exam?

[Hellrocks]

1) Both are accepted
2) It depends if the question says "show all bonds" in which O-H is needed as opposed to OH