© Prentice Hall 2001Chapter 21 Alkanes - Isomerism

© Prentice Hall 2001Chapter 22 Nomenclature Organic nomenclature is based on a class of compounds known as alkanes Contain only carbon and hydrogen All carbon atoms are sp 3 hybridized

© Prentice Hall 2001Chapter 23 Nomenclature International Union of Pure and Applied Chemistry (IUPAC) has established the system We will refer to names derived from this system as systematic nomenclature or IUPAC nomenclature (shown in blue) Additional names such as isopentane and neopentane are common names (shown in red) A compound may have more than one name BUT a name must specify only one compound

© Prentice Hall 2001Chapter 24 Nomenclature Typically any unspecified alkyl group is represented as R-

© Prentice Hall 2001Chapter 25 Nomenclature Alkyl substituent group names are combined as needed with the alkane name for the longest continuous straight chain to constitute a compound name Note that these compounds all have the formula C 7 H 16 ; they are isomers

© Prentice Hall 2001Chapter 26 IUPAC Systematic Nomenclature - Alkanes 1.Determine longest continuous chain (i.e. parent hydrocarbon) 2.Cite the name of substituent before the name of the parent hydrocarbon along with the number of the carbon to which it is attached

© Prentice Hall 2001Chapter 27 IUPAC Systematic Nomenclature - Alkanes 3.Number in the direction that gives the lower number for the lowest-numbered substituent. Substituents are listed in alphabetical order – neglecting prefixes such as di- tri- tert- etc.

© Prentice Hall 2001Chapter 28 IUPAC Systematic Nomenclature - Alkanes 4.When both directions yield the same lower number for the lowest numbered substituent, select the direction that yields the lower number for the next lowest numbered substituent

© Prentice Hall 2001Chapter 29 IUPAC Systematic Nomenclature - Alkanes 5.If same substituent numbers are obtained in either direction, number in direction giving lowest number to the first named substituent

© Prentice Hall 2001Chapter 210 IUPAC Systematic Nomenclature - Alkanes 6.If compound has two or more chains of the same length, parent hydrocarbon is chain with greatest number of substituents

© Prentice Hall 2001Chapter 211 IUPAC Systematic Nomenclature - Alkanes 7.Names such as sec-butyl and tert-butyl are acceptable, but systematic substituent names are preferable Numbering of the substituent begins with the carbon attached to the parent hydrocarbon This number together with the substituent name is placed inside parentheses

© Prentice Hall 2001Chapter 212 Alkyl Nomenclature A primary carbon is one that is bonded to only one other carbon, frequently represented by 1  A primary hydrogen is attached to a primary carbon

© Prentice Hall 2001Chapter 213 Alkyl Nomenclature A secondary carbon is one that is bonded to two other carbons, represented by 2 , also by sec- or s- A secondary hydrogen is attached to a secondary carbon

© Prentice Hall 2001Chapter 214 Alkyl Nomenclature A tertiary carbon is one that is bonded to three other carbons, represented by 3 , also by tert- or t- A tertiary hydrogen is attached to a tertiary carbon

© Prentice Hall 2001Chapter 215 Alkyl Nomenclature Reactivity often depends on whether a carbon or hydrogen is 1 , 2 , or 3 

© Prentice Hall 2001Chapter 216 Nomenclature of Cycloalkanes Cycloalkanes generally are shown as skeletal structures

© Prentice Hall 2001Chapter 217 Nomenclature of Cycloalkanes 1.Ring is the parent hydrocarbon unless the alkyl substituent has more carbons; in that case the substituent becomes the parent hydrocarbon If only one substituent, no need to give it a number

© Prentice Hall 2001Chapter 218 Nomenclature of Cycloalkanes 2.If the ring has 2 substituents, list in alphabetical order and give number 1 to first named group

© Prentice Hall 2001Chapter 219 Nomenclature of Cycloalkanes 3.If there is more than one substituent, list in alphabetical order; one substituent is given the position number 1; number either clockwise or counterclockwise - lowest numbers