How do i name alkenes?

Question

here are some examples:

HEXENE C6H12
CH2=CH-CH2-CH2-CH2-CH3
1 - HEXENE

CH3-CH=CH-CH2-CH2-CH3
2 - HEXENE

CH3-CH2-CH=CH-CH2-CH3
3 - HEXENE


CH2=C-CH2-CH2-CH3
-CH3
2 METHYL 2 PENTENE

HOW DO YOU NAME THESE ALKENES?
SURE I HAVE THEIR NAMES BUT HOW DID MY TEACHER GET THESE NAME?
WHAT ARE THE RULES,STEPS TO GET THE NAMES OF THE ALKENES?

CH2=C-CH2-CH2-CH3
l
CH3
2 METHYL 2 PENTENE

Answer 1

A brief guide to alkene nomenclature

The primary suffix name (..ene for C=C bond) is based on the longest carbon chain: 2 carbons, ethene; 3 carbons, propene; 4 carbons, butene. After these 4 preserved 'old trivial' names, the name is 'numerically' systematic e.g. 5 carbons, pentene; 6 hexene, 7 heptene etc.
If the molecule has a ring of carbon atoms including the double bond, the name is prefixed by cyclo….
Beyond propene, numbers (e.g. x or y) are needed to indicate the position of the double bond (e.g. …..-x-ene) or more than one double bond (e.g. …..-x,y-diene). These numbers take precedence over substituent numbers and they indicate, via lowest possible number, the first carbon of each C=C double bond.
The positions of the substituent(s), denoted with a prefix e.g. halo… or alkyl… groups, are denoted by using the lowest possible numbers for the associated carbon atoms in the main chain BUT these 'lowest' numbers are determined by the number assigned to the ene group.
If there is more than one 'type' of substituent e.g. using the prefixes: bromo…, chloro…, methyl… etc., they are written out in alphabetical order irrespective of carbon atom number (note: di, tri are ignored in using this rule).
There is a brief note on the formation and structure of poly(alkenes) and the name of the poly(alkene) is readily derived e.g. poly(ethene) [old/everyday names 'polyethylene'/'polythene'] or poly(propene) [old/everyday names 'polypropylene'/'polypropene']
Some 'old' names are quoted in () though their use should be avoided if possible [but many still used - just put one into GOGGLE!].

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Note on the homologous series of Alkenes

The open chain alkenes with one 'ene' group have the general formula CnH2n (see examples 1, 2, 6), they are isomeric with cycloalkanes from C3 onwards
The open chain alkenes with two 'ene' groups, i.e. dienes, have the general formula CnH2n-2 (see examples 4 and 17)
The cycloalkenes with one 'ene' group in the ring also have the general formula CnH2n-2 (see examples 5 and 19)
The cycloalkenes with two 'ene' groups i.e. cyclodienes, in the ring have the general formula CnH2n-4 (see example 20)
There are many structural isomers in all the above groups, either of the form of chain, positional or functional group isomerism.
Some 'old' names are quoted in () though their use should be avoided if possible [but many still used - just put one into GOGGLE!].


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Examples of Alkenes

The simplest alkene is ethene (ethylene), molecular formula of , structural formulae are
or and the skeletal formula is only !
a substituted ethene: chloroethene (old name 'vinyl chloride'), C2H3Cl, CH2=CHCl
The next open chain alkene is propene (propylene),
, , , , ,
1-chloropropene or 1-chloroprop-1-ene: CH3-CH=CHCl
2-chloropropene or 2-chloroprop-1-ene: CH3-CCl=CH2

3-chloropropene or 3-chloroprop-1-ene: ClCH2-CH=CH2

Methylpropene or 2-methypropene, but 2- is not really needed here, (isobutene, isobutylene), is the simplest branched open chain alkene, , ,
Propadiene, (propa-1,2-diene, but the numbers NOT needed), is the simplest possible open chain 'diene', that is, with two C=C double bonds in the molecule,
, , ,
The simplest cycloalkene is cyclopropene, , , ,
But-1-ene (1-butene) is the first alkene, without substituent groups, where a positional number is needed,
,
1-chlorobut-1-ene: CH3-CH2-CH=CHCl
2-chlorobut-1-ene: CH3-CH2-CCl=CH2

3-chlorobut-1-ene: CH3-CHCl-CH=CH2

4-chlorobut-1-ene: ClCH2-CH2-CH=CH2

2-methylbut-1-ene, ,
3-methylbut-1-ene, , ,
2,3-dimethylbut-1-ene, ,
3,3-dimethylbut-1-ene, ,
2,3,3-trimethylbut-1-ene, ,
But-2-ene (2-butene) is the first alkene (with no substituent groups) to have geometrical isomers of
, , but the latter doesn't show the two different spatial arrangements possible due to a high energy barrier to rotation about the double bond,
or is cis-but-2-ene,
or is trans-but-2-ene,
in simple cases, with two identical/similar groups, the trans isomer has these groups 'diagonally' opposite and the cis isomer has the groups at a 'right angle' to each other)
1-chlorobut-2-ene: CH3-CH=CCl-CH2Cl

2-chlorobut-2-ene: CH3-CH=CHCl-CH3

2-methylbut-2-ene, does not have geometrical isomers because there are two identical groups (CH3) attached to the same carbon of the double bond,

, , does not have geometrical isomers because there are two identical groups (CH3) attached to the same carbon of the double bond,

2,3-dimethylbut-2-ene, , , does not have geometrical isomers because there are two identical groups attached to the same carbon of the double bond,

buta-1,2-diene (note the a after the but), is the next simplest diene after propadiene, i.e. with two C=C double bonds,

, , ,

buta-1,3-diene (note the optional a after the but), is the next diene i.e. 2 C=C double bonds and isomeric with buta-1,2-diene (above),

, , and has two geometrical isomers,

cis-buta-1,3-diene

, and

trans-buta-1,3-diene ,

(2-methylbuta-1,3-diene is the synthetic rubber 'isoprene')

Cyclobutene is the next simplest cyclo-alkene after cyclopropane

, , ,

Cyclobuta-1,3-diene is the simplest cyclo-diene that exists, , ,

Pent-1-ene, , ,

2-methylpent-1-ene, ,

3-methylpent-1-ene, ,

4-methylpent-1-ene, ,

2,3-dimethylpent-1-ene, ,

2,4-dimethylpent-1-ene, ,

3,3-dimethylpent-1-ene, ,

3,4-dimethylpent-1-ene, ,

4,4-dimethylpent-1-ene, ,

3-ethylpent-1-ene, ,

Pent-2-ene, , , has geometrical isomers:

cis- and trans-

2-methylpent-2-ene, , , has geometrical isomers.

3-methylpent-2-ene, , has two geometrical isomers:

, ,

and ,

4-methylpent-2-ene, , has two geometrical isomers:

cis- , , trans-

2,3-dimethylpent-2-ene,

2,4-dimethylpent-2-ene,

3,4-dimethylpent-2-ene, ,

it has two geometrical isomers: cis- , and trans

4,4-dimethylpent-2-ene, , has two geometrical isomers:

cis- , and trans-

3-ethylpent-2-ene, , ,

no geometrical isomers because there are two identical groups attached to the same carbon of the double bond

Cyclopentene, , ,

Cyclopenta-1,3-diene, ,

Hex-1-ene, , ,

2-methylhex-1-ene, ,

42. - 46. have no geometrical isomers because there are two identical groups (H) attached to the same carbon of the double bond.

3-methylhex-1-ene, ,

4-methylhex-1-ene, ,

5-methylhex-1-ene, ,

Hex-2-ene, , two geometrical isomers:

cis- , , and

trans-, ,

2-methylhex-2-ene, ,

3-methylhex-2-ene, ,

has two geometrical isomers: and

4-methylhex-2-ene, ,

has two geometrical isomers: cis- , and trans-

5-methylhex-2-ene, , has two geometrical isomers:

cis- and trans-

Hex-3-ene, , has two geometrical isomers:

cis- , trans-

2-methylhex-3-ene, , has geometrical isomers:

cis- and trans-

3-methylhex-3-ene, has geometrical isomers:

cis- and trans-

Cyclohexene, , ,

Cyclohexa-1,3-diene, ,

Cyclohexa-1,4-diene, , ,

hept-1-ene, , , , no geometrical isomers

hept-2-ene, , ,

has geometrical isomers: cis- and trans-

hept-3-ene, ,

has geometrical isomers: cis- and trans-



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APPENDIX 1. The general equation for the formation of a poly(alkene)





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APPENDIX 2. Short note on Alkyne structure and naming

ALKYNES are unsaturated hydrocarbons with a CC triple bond CC triple bond

examples: ethyne (acetylene)

propyne (methylacetylene).



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APPENDIX 3. The naming and structure of some simple chloroalkenes

chloroethene

1-chloropropene

2-chloropropene

3-chloropropene

1-chlorobut-1-ene

2-chlorobut-2-ene

3-chlorobut-1-ene

4-chlorobut-1-ene

1-chlorobut-2-ene

2-chlorobut-2-ene



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SITE PURPOSE: EDUCATION-SCIENCE-ORGANIC CHEMISTRY REVISING at Doc Brown's Chemistry Clinic via HOMEPAGE in school, college or home. This page offers some practice in studying organic structure and nomenclature e.g. here the naming and graphical structure of alkenes and chloroalkenes using molecular formula, abbreviated, full graphic and skeletal structures. The website is designed to help students/teachers revise, learn or teach the chemistry for for modular or co-ordinated examination science courses from UK QCA based AQA, OCR, Edexcel, Nuffield, Salters, Cambridge, London International, WJEC, CCEA etc. examinations for Advanced Subsidiary GCE-AS-A2-IB-KS5 levels and covers much of the revising, learning and teaching chemistry of the International Baccalaureate,K12 US grade 10,11,12,AP basic level examinations for the national curriculum for secondary schools and colleges. Dr W P Brown

Answer 2

Where it's just a straight chain, you count the number of bonds over to the double bond, starting with the shortest end. So, 2-hexene: The double bond is the second bond along the chain. In 3-hexene, it's the third bond along the chain.
you can also call them hex-1-ene, hex-2-ene etc.
Where it's a branched chain, you have to figure out what is the longest straight section of it. So, in the case of 2-methyl-2-pentene the longest straight part of it is 5 carbons long, hence 'pentene'; ('pent' meaning 5, 'hex' meaning 6, etc).
In addition to the straight chain, there is a methyl substituent on the second carbon along the chain. So it's '2-methyl'. The double bond is the second bond along the chain, so overall it's 2-pent-2-ene.

Answer 3

alkene r nothing but contaning only carbon n hydrogen basically there r pri, sec n tertiary alkene 1st step is to count the no. of carbon eg, if there r 4 carbon we name it as butene 2nd step numbering the chain start numbering where the double bond is close eg. CH3-CH2=CH2-CH2-CH3 in this numbering will be frm left side

Answer 4

its like this:

that first one has a double bond in position 1 so its 1,hexene
that third one 3, hexene cuz the double bond is in the third position

if it was in the 5th position then reverse it, same as 2, hexene

the last example is difficult since typing restricts the picture