* GCE Advanced Organic Chemistry  NAMING & STRUCTURE of ALKENES at Doc Brown's

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 Doc Brown's Chemistry  Revising Organic Chemistry

The molecular structure and naming-nomenclature of ALKENES

including cycloalkene hydrocarbons and isomers of the same molecular formula (including geometrical isomers) and a brief appendix on poly(alkenes), ALKYNES and chloroalkenes

Examples of displayed formula of alkene molecules, graphic formula, molecular formula, skeletal formula, structural formula of this homologous series

Revision notes for GCE Advanced Subsidiary Level AS Advanced Level A2 IB Revise AQA GCE Chemistry OCR GCE Chemistry Edexcel GCE Chemistry Salters Chemistry CIE Chemistry revising courses for pre-university students (equal to US grade 11 and grade 12 and Honours/honors level courses)

m/c quiz on naming alkenes * type in name quiz on alkenes * organic functional group tests

summary of functional groups * EMAIL query?comment

The shapes and bond angles of simple molecules - section on bond angles in organic molecules


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.
    • e.g. alkenes structure and naming (c) doc b propene, and
    • alkenes structure and naming (c) doc bpent-1-ene (1-pentene, IUPAC allowed and typically used in US etc.)
    • I'm afraid several variations of nomenclature are allowed by the IUPAC which can make naming a bit confusing at times!)
  • If the molecule has a ring of carbon atoms including the double bond, the name is prefixed by cyclo
    • e.g. alkenes structure and naming (c) doc bcyclohexene and alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b
    • cyclopenta-1,3-diene (1,3-cyclopentadiene)
  • Beyond propene, numbers (e.g. x and y) are needed to indicate the position of the double bond (e.g. …..-x-ene, like pent-1-ene above) or more than one double bond (e.g. …..-x,y-diene, like penta-1,3-diene above and buta-1,3-diene below). These numbers take precedence over substituent numbers and they indicate, via lowest possible number, the first carbon of each C=C double bond which is a higher ranking group than the substituent groups.
    • e.g.alkenes structure and naming (c) doc b hex-3-ene (e.g. in UK, 3-hexene in US)
    • or alkenes structure and naming (c) doc b buta-1,3-diene (e.g. in UK, 1,3-butadiene in US)
  • The positions of the substituent(s), denoted with a prefix, e.g. halo… for chloro etc. or alky groups like methyl, ethyl etc., are denoted by using the lowest possible numbers for the associated carbon atoms in the main chain BUT these 'lowest' substituent numbers are determined by the number assigned to the ....ene group, so they can end up seeming a bit high because of the higher ranking ...ene functional group.
    • e.g. alkenes structure and naming (c) doc b
    • 5-methylhex-1-ene, the alkene functional group (C1) is higher ranking than the substituent methyl group (on C5),
    • or alkene (c) doc b  3-chlorobut-1-ene, which is NOT 2-chloro-but-1-ene or 2-chloro-but-2-ene or 2-chloro-but-3-ene etc.
  • 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!].
  • The IUPAC nomenclature for naming cis/trans geometrical isomers, or more correctly now, E/Z isomerism notation, is fully explained with examples in Isomerism Section 2. Stereoisomerism.
  • The shapes and bond angles of simple molecules - section on bond angles in organic molecules


Note on the homologous series of Alkenes

  • The open chain alkenes with one 'ene' group have the general formula CnH2n (n = 2, 3, 4 etc.), they are isomeric with cycloalkanes from C3 onwards.
    • n must be >1 to give a C=C double bond.
  • The open chain alkenes with two 'ene' groups, i.e. dienes, have the general formula CnH2n-2 (n = 3, 4, 5 etc.)
    • n must be >2 to give two carbon-carbon double bonds.
  • The cycloalkenes with one 'ene' group in the ring also have the general formula CnH2n-2 (n = 3, 4, 5 etc.)
    • n must be >3 to give a ring, although cyclopropene is very unstable due to the C-C-C bond angle strain.
  • The cycloalkenes with two 'ene' groups i.e. cyclodienes, in the ring have the general formula CnH2n-4 (n = 4, 5, 6 etc.)
    • Propadiene does not exist (n = 3) because there is two much strain on the C-C-C bond angle if two of the three carbon-arbon bonds are doubles.
  • There are many structural isomers in all the above series, 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!].

TOP links


Examples of Alkenes

The simplest alkene is ethene (ethylene), molecular formula of alkenes structure and naming (c) doc b, structural formulae are

  •  alkenes structure and naming (c) doc bor alkenes structure and naming (c) doc band the skeletal formula is only alkenes structure and naming (c) doc b!
    • All bond angles 120o, symmetrical planar molecule
  • a substituted ethene: chloroethene (old name 'vinyl chloride'), C2H3Cl,  CH2=CHCl

     

The next open chain alkene is propene (propylene),

  • alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b
    • There are three monochloro substituted propenes
    • 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-methylpropene, but 2- is not really needed here, (isobutene, isobutylene), is the simplest branched open chain alkene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

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,

  • alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

The simplest cycloalkene is cyclopropene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

 

But-1-ene (1-butene) is the first alkene, without substituent groups, where a positional number is needed,

  • alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b
  • There four substituted monochloro but-1-enes
  • 1-chlorobut-1-ene:  CH3-CH2-CH=CHCl, 1-chloro-1-butene

    2-chlorobut-1-ene:  CH3-CH2-CCl=CH2, 2-chloro-1-butene

    3-chlorobut-1-ene:  CH3-CHCl-CH=CH2, 3-chloro-1-butene

    4-chlorobut-1-ene:  ClCH2-CH2-CH=CH2, 4-chloro-1-butene

     

2-methylbut-1-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b 2-methyl-1-butene

 

3-methylbut-1-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b 3-methyl-1-butene

 

2,3-dimethylbut-1-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b 2,3-dimethyl-1-butene

3,3-dimethylbut-1-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b TOP links3,3-dimethyl-1-butene

2,3,3-trimethylbut-1-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b 2,3,3-trimethyl-1-butene

But-2-ene (2-butene) is the first alkene (with no substituent groups) to have geometrical isomers (now correctly termed E/Z isomerism)

  •  alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, but the latter doesn't show the two different spatial arrangements possible due to a high energy barrier to rotation about the double bond

     

  • alkenes structure and naming (c) doc bor alkenes structure and naming (c) doc bis Z-but-2-ene, cis-2-butene etc.

     

  •  alkenes structure and naming (c) doc bor alkenes structure and naming (c) doc bis E-but-2-ene, trans-2-butene etc.

     

  • in simple cases, with two identical/similar groups, the E/trans isomer has these groups 'diagonally' opposite each other across the double bond and the Z/cis isomer has the groups at a 'right angle' to each other or on the same side of the plane of the double bond).
  • For a full explanation with examples see Isomerism Section 2. Stereoisomerism.
    • The are two monochlorosubstitued but-2-enes
    • 1-chlorobut-2-ene:  CH3-CH=CH-CH2Cl, 1-chloro-2-butene
    • 2-chlorobut-2-ene:  CH3-CH=CCl-CH3

    • , 2-chloro-2-butene

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,

  • alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

  • 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, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, 2,3-dimethyl-2-butene, 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,

  •  alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

  • , 1,2-butadiene

     

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

  • alkenes structure and naming (c) doc b,alkenes structure and naming (c) doc b , and has two geometrical isomers,

     

  •  alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc bZ/cis-buta-1,3-diene,

     

  • alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b E/trans-buta-1,3-diene

  • 2-methylbuta-1,3-diene is the synthetic rubber 'isoprene'.

Cyclobutene is the next simplest cyclo-alkene after cyclopropene

  • alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

Cyclobuta-1,3-diene is the simplest cyclo-diene that exists, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b TOP links

Pent-1-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b 1-pentene

 

  • A selection of methyl substituted methylpent-1-enes and an ethylpent-1-ene

  • 2-methylpent-1-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

  • 2-methyl-1-pentene

  • 3-methylpent-1-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

  •  3-methyl-1-pentene

  • 4-methylpent-1-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

  •  4-methyl-1-pentene

  • 2,3-dimethylpent-1-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

  •   2,3-dimethyl-1-pentene

  • 2,4-dimethylpent-1-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

  •   2,4-dimethyl-1-pentene

  • 3,3-dimethylpent-1-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

  •   3,3-dimethyl-1-pentene

  • 3,4-dimethylpent-1-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

  •   3,4-dimethyl-1-pentene

     

  • 4,4-dimethylpent-1-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

  •   4,4-dimethyl-1-pentene

  • 3-ethylpent-1-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

  • TOP links3-ethyl-1-pentene

Pent-2-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, 2-pentene two geometrical isomers:

  • Z/cis- alkenes structure and naming (c) doc band E/trans- alkenes structure and naming (c) doc b

  •  

  • A selection of methyl substituted pent-2-enes and an ethylpent-2-ene

  • 2-methylpent-2-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

  • 2-methyl-2-pentene has no geometrical isomers

  • 3-methylpent-2-ene, alkenes structure and naming (c) doc b, 3-methyl-2-pentene, has two E/Z or geometrical isomers:

    •  alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, Z-3-methylpent-2-ene

    • and   alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

    • E-3-methylpent-2-ene

  • 4-methylpent-2-ene, alkenes structure and naming (c) doc b, has two geometrical isomers:

    • Z/cis- alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, E/trans- alkenes structure and naming (c) doc b

  • 2,3-dimethylpent-2-ene, alkenes structure and naming (c) doc b

  • (2,3-dimethyl-2-pentene)

  • 2,4-dimethylpent-2-ene, alkenes structure and naming (c) doc b

  • (2,4-dimethyl-2-pentene)

  • 3,4-dimethylpent-2-ene, alkenes structure and naming (c) doc b(3,4-dimethyl-2-pentene)

    • has two geometrical isomers: E-alkenes structure and naming (c) doc b , and Z- alkenes structure and naming (c) doc b

    • 3,4-dimethylpent-2-ene

       

  • 4,4-dimethylpent-2-ene, alkenes structure and naming (c) doc b  (4,4-dimethyl-2-pentene) has two geometrical isomers:

    • Z/cis- alkenes structure and naming (c) doc b, and E/trans- alkenes structure and naming (c) doc b

  • 3-ethylpent-2-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b (3-ethyl-2-pentene)

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

cyclopentene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b TOP links

 

cyclopenta-1,3-diene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b (1,3-cyclopentadiene)

hex-1-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b  (1-hexene)

2-methylhex-1-ene, alkenes structure and naming (c) doc balkenes structure and naming (c) doc b (2-methyl-1-hexene)

  • There are no geometrical isomers of -1-enes because there are two identical groups (H) attached to the same carbon of the double bond

  • .

     

  • You can also put a methyl substituent on carbons 3, 4 and 5

  • 3-methylhex-1-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

  •   (3-methyl-1-hexene)

  • 4-methylhex-1-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

  •   (4-methyl-1-hexene)

  • 5-methylhex-1-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

  • (5-methyl-1-hexene)

Hex-2-ene, alkenes structure and naming (c) doc b, 2-hexene has two geometrical isomers:

  • Z/cis- alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, and

  • E/ trans-, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

  •  

  • There are four monosubstituted methylhex-2-enes

  • 2-methylhex-2-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

  • (2-methyl-2-hexene)

  • 3-methylhex-2-ene, alkenes structure and naming (c) doc b,

    • has two geometrical isomers: E-alkenes structure and naming (c) doc band Z-alkenes structure and naming (c) doc b

    • (3-methyl-2-hexene)

  • 4-methylhex-2-ene, alkenes structure and naming (c) doc b,

    • has two geometrical isomers: Z/cis- alkenes structure and naming (c) doc b, and E/trans- alkenes structure and naming (c) doc b

    • TOP links

  • 5-methylhex-2-ene, alkenes structure and naming (c) doc b, has two geometrical isomers:

     Z/cis- alkenes structure and naming (c) doc band E/trans- alkenes structure and naming (c) doc b

Hex-3-ene, alkenes structure and naming (c) doc b, 3-hexene has two geometrical isomers:

  • Z/cis- alkenes structure and naming (c) doc b, E/trans- alkenes structure and naming (c) doc b

  •  

  • and two mono substituted methylhex-3-enes

  • 2-methylhex-3-ene, alkenes structure and naming (c) doc b, has geometrical isomers:

    •  Z- alkenes structure and naming (c) doc band E- alkenes structure and naming (c) doc b

    • (2-methyl-3-hexenes)

  • 3-methylhex-3-ene, alkenes structure and naming (c) doc bhas geometrical isomers:

    • Z- alkenes structure and naming (c) doc band E- alkenes structure and naming (c) doc b

    •  3-methyl-3-hexene

cyclohexene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

 

cyclohexa-1,3-diene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b  (cyclohexa-1,3-diene or 1,3-cyclohexadiene)

cyclohexa-1,4-diene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b (cyclohexa-1,4-diene or 1,4-cyclohexadiene)

hept-1-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

1-heptene has no geometrical isomers

hept-2-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b,

  • has geometrical isomers: Z/cis- alkenes structure and naming (c) doc band E/trans- (c) doc b

  • (2-heptene)

hept-3-ene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

  • has geometrical isomers: Z/cis- alkenes structure and naming (c) doc band E/trans- alkenes structure and naming (c) doc b (3-heptene)

TOP links


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

alkenes structure and naming (c) doc b

TOP links


APPENDIX 2. Short note on Alkyne structure and naming

  • ALKYNES are unsaturated hydrocarbons with a Calkene (c) doc bC triple bond

    • examples: alkene (c) doc b ethyne (acetylene)

    • alkene (c) doc b propyne (methylacetylene).

TOP links


APPENDIX 3. Summary of the naming and structure of some simple chloroalkenes

  1. alkene (c) doc b  chloroethene

  2. alkene (c) doc b  1-chloropropene

  3. alkene (c) doc b  2-chloropropene

  4. alkene (c) doc b  3-chloropropene

  5. alkene (c) doc b  1-chlorobut-1-ene (1-chloro-1-butene)

  6. alkene (c) doc b  2-chlorobut-1-ene (2-chloro-1-butene)

  7. alkene (c) doc b  3-chlorobut-1-ene (3-chloro-1-butene)

  8. alkene (c) doc b  4-chlorobut-1-ene (4-chloro-1-butene)

  9. alkene (c) doc b 1-chlorobut-2-ene (1-chloro-2-butene)

  10. alkene (c) doc b  2-chlorobut-2-ene (2-chloro-2-butene)


C2H4 CH2=CH2 C3H4 C3H6 C4H4 C4H6 C4H8 CH2=CHCH2CH3 CH3CH=CHCH3 C5H8 C5H10 C6H12


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(portuguese) Doc Brown de Revisão Química Química Orgânica A estrutura molecular ea nomenclatura, nomes de alcenos incluindo os hidrocarbonetos cicloalqueno e isômeros da mesma fórmula molecular (incluindo os isômeros geométricos) e um breve apêndice sobre poli (alquenos) , alcinos e chloroalkenes Exemplos de fórmulas indicadas de moléculas de alqueno, a fórmula de gráfico, fórmula molecular, a fórmula do esqueleto, a fórmula estrutural da série homóloga * (spanish) Doc Brown Revisión Química Orgánica La estructura molecular y la denominación-la nomenclatura de los alquenos incluidos los hidrocarburos Cicloalqueno e isómeros de la misma fórmula molecular (incluidos los isómeros geométricos) y un breve apéndice de poli (alquenos) , alquinos y chloroalkenes. Ejemplos de la fórmula muestra de moléculas de alqueno, fórmula desarrollada, fórmula molecular, la fórmula del esqueleto, la fórmula estructural, de esta series homólogas * (polish) Doc Brown Poprawianie Chemii Chemii Organicznej Struktury molekularnej i nazywanie nomenklatury alkenów tym Cykloalkeny węglowodorów i izomerów tego samego wzoru cząsteczkowej (w tym izomerów geometrycznych), krótki dodatek na poli (alkenów) , alkinów i chloroalkenes Przykłady wyświetlane formule cząsteczki alkenu, wzór graficzny, wzór cząsteczkowy, formuła szkieletowych, wzór strukturalny tego serii homologicznych Podstawowej nazwy przyrostek (.. ene obligacji na C = C) opiera się na najdłuższy łańcuch węglowy: 2 węgle, eth ene, 3 atomów węgla, wniosku ene; 4 atomów węgla, ale ene. After these 4 preserved 'old trivial' names, the name is 'numerically' systematic eg 5 carbons, pent ene ; 6 hex ene , 7 hept ene etc. Po tych 4 zachowanych starych trywialne "imiona, imię" numerycznie "systematyczne np. 5 atomów węgla, pent ene, 6 hex ene, 7 hept ene itp * (german) Doc Brown's überarbeiten Chemie Organische Chemie Die molekulare Struktur und Namensgebung-Nomenklatur von Alkenen einschließlich Cycloalken Kohlenwasserstoffe und Isomere der gleichen Summenformel (einschließlich geometrischer Isomere) und einem kurzen Anhang über Poly (Alkene) , Alkine und Chloralkenen Beispiele angezeigten Formel von Alken-Moleküle, Grafik, Summenformel, Skelett-Formel, Strukturformel dieser homologen Reihe Eine kurze Anleitung zum Alken Nomenklatur Der primäre Suffix-Namen (.. ene für C=C-Bindung) ist Kette auf der Grundlage der längsten Kohlenstoff: 2 C -Atomen, ETH ene, 3 Kohlenstoffe, prop ene; 4 Kohlenstoffatomen, doch ene. After these 4 preserved 'old trivial' names, the name is 'numerically' systematic eg 5 carbons, pent ene ; 6 hex ene , 7 hept ene etc. Nach diesen 4 erhaltenen alten trivial 'Namen, Name ist der "numerisch" systematische zB 5 Kohlenstoffen, aufgestaute ene, 6 hex ene, 7 hept ene etc. *  
DOC'S PICTURES - always travel with my camera! images and notes