Alkenes or Olifins

Some Common alkenes or olifins
Alkenes or Olefins

Unsaturated Hydrocarbon:

    The compounds contain at least one pair of adjacent carbon atoms linked by multiple bonds, then that compound is said to be unsaturated.

Ethylene(C₂H₄):

      This Compound contains a double bond. There are only four univalent hydrogen atoms present in ethylene, therefore ethylene said to be unsaturated Compound.
      H₂C = CH₂

    Acetylene(C₂H₂):

      This Compound contains a triple bond and there are only two univalent hydrogen atoms.
      HC ☰ CH

    Alkenes or Olefins:

      The alkenes are the unsaturated hydrocarbons that contain one double bond. They have the general formula CnH2n, as they contain two hydrogen atoms less than the alkanes, alkenes are called unsaturated hydrocarbons. The double bond is called 'olefinic bond or 'ethylenic bond'.
      The name olefin arose from the fact that ethylene was called 'olefiant gas'( oil-forming gas) since it forms oily liquids when treated with chlorine or bromine.
      The original name given to this homologous series was olefine, but it was later decided to reserve the suffix -ine for basic substances only.

    Nomenclature of Alkenes:

    • Common naming of alkenes:
      In the common naming system of an olefin is named according to the following rules,
    1. The total number of carbon atom in the olefin is counted and the name of the corresponding alkane is determined.
      H2C=CH2 Corresponding alkane is ethane.
    2. By changing the name of the corresponding alkane, the suffix -ane of the latter into -ylene.
      For ethane changing the suffix -ane of the latter into -ylene.
    3. The position of the double bond is indicated by Number 1, 2, 3, 4...., or Greek Letters α, β, ⋎, ઠ, ...., the end carbon atom nearest to the double bond is denoted by 1, next 2,and so on or α, next β, and so on.
      These letters are then known as locants.
    4. The locants of the double bond carbon atom are then placed before the name of the olefin as obtain from rule 1 and 2.
      A hyphen is written in between the locants and the name.
      The locants are used only to name olefins containing more than three carbon atom. Olefins of low molecular weights only have common names.
    Common naming of alkenes or olifins
    Common naming of alkenes
    • Problem 1:
      Write down the common names of the following compounds: (i) CH3CH2CH2CH=CH2 (ii) CH3CH=CHCH2CH3.
    • Answer:
      (i) CH₃ - CH₂ - CH₂ - CH=CH2
      Parent alkane is pentane. Thus the name of the Compound is, 1 - pentylene or α - pentylene
      (ii) CH3 - CH = CH - CH2 - CH3
      Parent alkane is pentane Thus the name of the Compound is 2 -pentylene or β - pentylene
    • Substituted or derived naming of alkenes:
      Another method of nomenclature is to consider ethylene as the parent substance and higher member is derivatives of ethylene.
      If the compound is mono-substituted then no difficulty arises in naming. But the compound is a disubstituted derivative of ethylene isomerism is possible. Since the alkyl groups are of attached same or different carbon atoms.
      When the groups are attached to the same carbon atom of the olefins named as the asymmetrical compound.
      When the groups are attached to the different carbon atom of the olefins named as the symmetrical compound.
      CH3 ㄧCH = CH2 Methylethylene 
      CH3ㄧCH2ㄧCH = CH2 Ethylethylene
      CH3 ㄧ(H3C)C = CH2 as - dimetylethylene
      CH3ㄧCH = CHㄧCH3 sym - dimethylethylene
    • I.U.P.A.C. naming of alkenes:
      According to the I.U.P.A.C. system of nomenclature, the class suffix of the olefins is - ene, and so the series becomes the alkene series.
    1. The longest carbon chain containing the double bond is chosen as the parent alkene.
      CH₃C(CH₃)₂CH₂CH(CH₃)CH=C(CH₃)CH₂CH₃
      The parent part is here base chain, it consists of 8 carbons. The base name, therefore, is to be derived from octane.
    2. The position of the double bond and side chains are indicated by numbers, the lowest number possible being given to the double bond, and this is placed before the suffix.
    3. IUPAC naming alkenes or Olifins
      IUPAC naming alkenes
    4. The name of which is obtained by changing the suffix - ane of the corresponding alkane into - ene.
      To give the lowest number of possible double bonded carbon is numbered 3.
      There are four branches, One methyl branch on carbon atom number 3, three methyl branches on 5th and 7th carbon atoms. These are to be indicated as prefixes to the base name. Their names with their locants are 3, 5, 7, 7 - tetramethyl.
      Hence the full name is,
    3, 5, 7, 7 - tetramethyl - 3 - octene
    • Problem 2:
      What are the names of the following compounds in the IUPAC system ? (i) CH3 - CH2 - CH = CH2 (ii) C(CH3)2 = CH2 (iii) CH3 - CH = C(CH3) - CH2 - CH3 (iv) CH2 = C(C2H5) - CH(CH3)2
    • Answer:
      (i) CH₃ - CH₂ - CH = CH₂ but-1-ene
      (ii) (CH₃)₂C = CH₂ 2-methylprop-1-ene
      (iii) CH₃ - CH = C(CH₃) - CH₂ - CH₃ 3-methylpent-2-ene
      (iv) CH₂ = C(C₂H₅) - CH(CH₃)₂ 2-ethyl-3-methylbut-1-ene
    • Problem 3:
      Write out the (ignoring stereo-chemistry) of the isomeric pentenes, and name them by the IUPAC system. Give the structures of the products formed from each on Ozonolysis.
    • Answer:
      The Molecular formula of the pentene is C5H12.
      Now take each one in turn and introduce one double bond, starting at the least substituted end and shifting the double bond inwards.
      CH₃CH₂CH₂CH=CH₂ pent-1-ene 
      CH₃CH₂CH=CHCH₃ pent-2-ene
      CH₃CH(CH₃)CH=CH₂ 3-methylbut-1-ene
      CH₃C(CH₃)=CHCH₃ 2-methylbut-2-ene
      CH₃CH₂C(CH₃)=CH₂ 2-methylbut-1-ene
      The product obtained from the ozonide depends on the nature of the reagents used. Here we small use of Zn and acid to give aldehyde and/or ketones.
      CH₃CH₂CH₂CH=CH₂ CH₃CH₂CH₂CHO + HCHO
      CH3CH2CH=CHCH3 CH3CH2CHO + CH3CHO
      CH3CH(CH3)CH=CH2 CH3(CH3)CHCHO + HCHO
      CH3CH2C(CH3)=CH2 HCHO + CH3COCH2CH3
      CH3C(CH3)=CHCH3 CH3(CH3)C=O + CH3CHO

    Unsaturated Hydrocarbon, Alkenes or olifins, Common naming, Substituted or derived and I.U.P.A.C. naming of alkenes with problems and their solutions

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