1-Alkanes(praffinic compounds) • There are composed of only carbon atoms and hydrogen atoms and contain only single bonds(saturated hydrocarbons) • We can indicate this in the family name and in names for specific compounds by the -aneending. • The general formula CnH2n+2, where n is any integer. • The carbons form a continuous chain with no branches are called straight-chain alkanes while branched carbon chains called branched-chain alkanes
As the number of carbons in an alkane increases beyond three, the number of possible structures increases. There are two possible structures for an alkane with molecular formula, In addition to butane—a straight-chain alkane—there is a branchedbutane called iso butane. Examples: What is the molecular formula of an alkane with six carbon atoms? Solution If n = 6, then 2n +2 = 14. The formula is C6H14. PROBLEM :1 What is the molecular formula of an alkane with 12 carbon atoms? PROBLEM :2 Which of the following are alkanes? a. C7H16 b. C7 H12 c. C8H16 d. C29H60
Alkyl groups: If a hydrogen atom is removed from an alkane, the partial structure that remain is called alkyl group.) Note: An alkyl group is named by taking the name of the alkane with the same number of carbon atoms and changing the -aneending to -yl.
Note: Compounds which have the same formula but different structures are called isomers. It should be noted that primary carbon (1˚)is bonded to another carbon, secondary carbon (2˚) is bonded to two other carbons, tertiary carbon(3˚) and quaternary carbon (4˚) are bonded to 3 and 4 other carbons respectively.
The 3 isomers are : H HH │ │ │ H―C ―C ―O ―C ―H │ │ │ H HH │ │ │ ―C―C―C―O―H │ │ │ │ O │ │ │ ―C―C―C― │ │ │
Note: The letter Ris used as a general symbol for an alkyl group. The formula R-H, therefore represents any alkane. The formula R-Clstands for any alkyl chloride (methyl chloride, ethyl chloride, and so on). Halogen substituents are named by changing the -ineending of the element to -O.
((Alkane Nomenclature IUPAC Rules for Naming Alkanes 1-Alkanes without branches are named according to the number of carbon atoms .These names, up to ten carbons(table 2.1) 2-For alkanes with branches, the root name is that of the longest continuous chain of carbon atoms (parent chain) For example, in the structure: the longest continuous chain (in color) has five carbon atoms. The compound is therefore named as a substituted pentane, 3-Groups attached to the main chain are called substituents. Saturated substituents that contain only carbon and hydrogen are called alkyl group.
4-. Beginning at the end nearer the first branched points, number each carbon atom in the parent chain:
5-If two or more different types of substituents are present, they are listed Alphabetically. 6-If there is no third branch, begin numbering nearest the substituent whose name has alphabetic priority:
Draw the structure of 3-isopropyl-2-methyl hexane First: look at the parent name (hexane) and draw its carbon structure: C─C─C─C─C─C Next: find the substitutions (3-isopropyl and 2-methyl), and place them on the proper carbons
Assignment • Draw structures corresponding to the following IUPAC names : • (a) 3-Ethyl-4,4-dimethylheptane (b) 3,4-Dimethylnonane • Name the following structure of alkane