Ch03 notes orgo - Alkanes Alkanes are the simplest organic...

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Alkanes Alkanes are the simplest organic molecules, they only contain C and hydrogen, and only contain single bonds. Compounds that have the maximum number of bonded hydrogens, are said to be saturated. Alkanes are saturated hydrocarbons. General Formula: C n H 2n+2 The simplest members of this group are the n-alkanes. HC H H H H H C H H H H C H H H C H H H H C H H H C H H C CC H C H H H C H H C H H H H H H H H H methane C 1 H 4 ethane C 2 H 6 propane C 3 H 8 butane C 4 H 10 pentane C 5 H 12 The n-alkanes are straight chain molecules, but there are also branched alkanes (isomers). Ch03 Alkanes 1
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CC H C H H H C H H C H H H H H HC C CH 3 C H H H C H H H H H HH 3 CH 3 CH 3 CH 3 pentane C 5 H 12 isopentane C 5 H 12 neopentane C 5 H 12 Any series that differs only by an increasing number of –CH 2 - groups is known as a Homologous series . The individual members are said to be homologs of each other. Nomenclature of Alkanes There are two general types of nomenclature: trivial names (acetone, acetic acid) IUPAC System (propanone, ethanoic acid) IUPAC or Systematic Names The systematic way to name all organic compounds. For alkanes: (1) Find the longest continuous chain of carbon atoms. This is the base name of the compound. (2) Number the longest chain beginning with the end nearest a substituent. (3) Name the substituent groups attached to the longest chain as alkyl groups. Also state the location of each alkyl group according to its numbered carbon on the main chain. (4) When two or more substituents are present, list them in alphabetical order. If two or more of the same alkyl groups are present, use the prefixes di-, tri- etc to avoid repetition. Examples: CH 2 CH 3 CH-CH 2 -CH 2 -CH 3 H 3 C 3-methylhexane If there are two chains of equal length, choose the chain that has the highest number of substituents. Ch03 Alkanes 2
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CH 3 CH 2 H C HC H 3 C H C H 3 CH C CH 2 CH 3 CH 3 CH 3 CH 3 CH 2 H C HC H 3 C H C H 3 C CH 2 CH 3 CH 3 CH 3 Numbering starts at the end nearest a substituent so that the alkyl substituents have as low numbers as possible. CH 3 CH 2 H C HC H 3 C H C H 3 C CH 2 CH 3 CH 3 CH 3 CH 3 CH 2 H C HC H 3 C H C H 3 C CH 2 CH 3 CH 3 CH 3 Alkyl groups are named by replacing the –ane suffix of the alkane name with –yl. E.g. CH 3 CH 3 Ethane CH 3 CH 2 - Ethyl group CH 3 CH 2 CH 3 Propane CH 3 CH 2 CH 2 - Propyl group Common branched alkyl groups have trivial names: H 3 CC H 2 -CH 2 - H 3 C CH- CH 3 propyl isopropyl CH 3 CH 2 CH 2 CH 2 - CH 3 CH-CH 2 - H 3 C CH 3 CH 2 CH- CH 3 CH 3 C- H 3 C CH 3 butyl isobutyl sec-butyl tert-butyl t-butyl Ch03 Alkanes 3
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The names sec and tert are short for secondary and tertiary, referring to the degree of alkyl substitution. RC H H R H R R Primary 1 o carbon Secondary 2 o carbon Tertiary 3 o carbon Prefixes are used when there are more than one type of alkyl substituent Di = 2 Tri = 3 Tetra = 4 Penta = 5 The prefixes do not count when alphabetizing.
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Ch03 notes orgo - Alkanes Alkanes are the simplest organic...

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