Transcript Lecture_II
Alkanes - Isomerism Number of Carbons 6 Molecular Formula C6H14 Number of Isomers 5 7 C7H16 9 12 C12H26 75 15 C15H32 4347 © Prentice Hall 2001 Chapter 2 1 Nomenclature Organic nomenclature is based on a class of compounds known as alkanes Contain only carbon and hydrogen All carbon atoms are sp3 hybridized © Prentice Hall 2001 Chapter 2 2 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 2001 Chapter 2 3 Nomenclature Typically any unspecified alkyl group is represented as R© Prentice Hall 2001 Chapter 2 4 Nomenclature Alkyl substituent group names are combined as needed with the alkane name for the longest continuous straight chain to constitute a compound name © Prentice Hall 2001 Note that these compounds all have the formula C7H16; they are isomers Chapter 2 5 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 2001 Chapter 2 6 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 2001 Chapter 2 7 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 2001 Chapter 2 8 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 2001 Chapter 2 9 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 2001 Chapter 2 10 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 2001 Chapter 2 11 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 2001 Chapter 2 12 Alkyl Nomenclature A secondary carbon is one that is bonded to two other carbons, represented by 2, also by sec- or sA secondary hydrogen is attached to a secondary carbon © Prentice Hall 2001 Chapter 2 13 Alkyl Nomenclature A tertiary carbon is one that is bonded to three other carbons, represented by 3, also by tert- or tA tertiary hydrogen is attached to a tertiary carbon © Prentice Hall 2001 Chapter 2 14 Alkyl Nomenclature Reactivity often depends on whether a carbon or hydrogen is 1, 2, or 3 © Prentice Hall 2001 Chapter 2 15 Nomenclature of Cycloalkanes Cycloalkanes generally are shown as skeletal structures © Prentice Hall 2001 Chapter 2 16 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 2001 Chapter 2 17 Nomenclature of Cycloalkanes 2. If the ring has 2 substituents, list in alphabetical order and give number 1 to first named group © Prentice Hall 2001 Chapter 2 18 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 © Prentice Hall 2001 Chapter 2 19