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Topic: Naming&Drawing Hydrocarbons  (Read 12224 times)

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777888

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Naming&Drawing Hydrocarbons
« on: January 24, 2005, 10:09:28 AM »
1. 2-methyl-4-isopropylnonane
My questions:
(i)how would you draw the propyl group in the position 4? (what is iso?)
(ii)why isn't it in alphetical order? why "m"(methyl) goes before "i"(iso...)?

2. 3,5-dimethylcyclohexene
Do I have to identify the location of doulbe bond? There is a double bond but it's not shown in the name...why?

Please help me! Thanks!
« Last Edit: January 24, 2005, 10:09:53 AM by 777888 »

Offline Mitch

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Re:Naming&Drawing Hydrocarbons
« Reply #1 on: January 24, 2005, 11:21:48 AM »
2.) The -ene is the double bond
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Re:Naming&Drawing Hydrocarbons
« Reply #2 on: January 24, 2005, 03:16:12 PM »
2) The alkene is the highest priority group, so it must be at the 1 position.


This stuff should be covered in the first or second chapter of most every organic textbook.

777888

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Re:Naming&Drawing Hydrocarbons
« Reply #3 on: January 24, 2005, 03:20:34 PM »
2) The alkene is the highest priority group, so it must be at the 1 position.


This stuff should be covered in the first or second chapter of most every organic textbook.
SORRY, I still don't get it...

My school skipped organic in grade 11, but we are now learning organic(more advanced) in grade 12...I can't find any basic naming in the grade 12 text...so it's really hard for me :-\

1. 2-methyl-4-isopropylnonane
how would you draw the propyl group in the position 4? (what is iso?)
why isn't it in alphetical order? why "m"(methyl) goes before "i"(iso...)?

2. 3,5-dimethylcyclohexene
So I don't have to write the location of the double bond? what if there are 2 double bonds?

Thank you!
« Last Edit: January 24, 2005, 03:39:07 PM by 777888 »

dexangeles

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Re:Naming&Drawing Hydrocarbons
« Reply #4 on: January 24, 2005, 04:38:27 PM »
1)

isopropyl is the same as 1-methylethyl
isopropyl is a commo name, but still accepted by IUPAC
while 1-methylethyl is the IUPAC name

do you know how to draw bond-line formulas (carbon skeleton diagrams)?


2)

in cyclohexenes the double bond is in the C1-C2 location

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Re:Naming&Drawing Hydrocarbons
« Reply #5 on: January 24, 2005, 10:32:13 PM »
This site is pretty good for naming.  A few nice examples:

http://www.chemguide.co.uk/basicorg/conventions/names.html


Here are some of the basics:

a) The root is defined by the longest straight chain or largest ring.  In the case of problem 1, the root is nonane, which is a straight chain 9 carbons long.

b) Just about everything else is some kind of modifier to that root chain.  The numbers define the location.

c) The order that the substituents are listed is generally based on the number that they would be assigned, not alphabetical order.  So, methyl comes before isopropyl because the methyl is at the 2nd carbon from the end while the isopropyl is at the 4 position.

d) There are three modifiers that are becoming antiquated, but are still found in organic terminology.  You have to memorize them.  They are "normal" (or n-), "iso" (or i-, sometimes sec-), and "tertiary" (or t-, sometimes tert-).  When these modifiers come before the name of some alkyl group, they define how that group is arranged and bonded to the root chain.  As Dexangeles said, iso-propyl means a three carbon chain that is bonded at the central carbon instead of one of the end ones.  If it were bonded to one of the carbons on the end, it would be an n-propyl group.  Similarly an n-butyl group is a straight 4 carbon chain.  An iso-butyl group has the methyl group on the end shifted in one carbon, so it is more like a CH2 with an iso-propyl group.  A t-butyl group has all three methyl groups on the carbon that is bonded to the chain, so it is like a trimethyl-methyl group, or rather an isopropyl group with an extra methyl group.

e) Functional groups have been assigned a somewhat arbitrary "priority" ranking.  The proper name will always give the highest priority functional group the lowest number.  It is generally assumed that the highest priority group will be at the 1 position of a ring and so it isn't usually noted.  If there are multiple functional groups, you should always number the location of the functional group.


I hope this helps.  Let us know if you have more questions.

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