Chapter 21 Hydrocarbons Introduction to hydrocarbons 21-1 Organic molecules include most of the molecules that contain carbon. The simplest organic compounds are called hydrocarbons…they contain hydrogen and carbon. We will use models to represent organic molecules.

Chapter 21-1 (cont’d) We also use dot diagrams to represent organic molecules… structural dot diagram

Refining Hydrocarbons The process of fractional distillation is used to separate petroleum into the products we need and use.

Rating Gasoline Modern gasoline is a complex mixture of 5 to 12 carbon chains and additives to make the modern engines run efficiently. Octane rating , or antiknock rating, was established in the 1920’s.

21-2 Alkanes Straight-chain alkanes are named based upon the number of carbons linked together in a continuous chain. Alkanes have single bonds for their carbons. We use prefixes to indicate the number of carbons. Alkanes use a prefix followed by an –ane ending to tell that the molecules have single bonded carbons.

Prefixes Used to Name Organic Molecules Number of Carbons Name 1 methane 2 ethane 3 propane 4 butane 5 pentane 6 hexane 7 heptane 8 octane 9 nonane 10 decane 11 undecane 12 dodecane

Branched-Chain Alkanes Sometimes, there are side-groups added on to hydrocarbons…these are called substituent groups while the main chain is called the parent chain. The parent chain is the longest continuous chain of carbons in the molecule…remember, if the longest chain turns one or more corners, it is still the longest chain. The name reflects the address, or carbon, that the substituent group ‘lives’ on.

Substituent Carbon Groups

Other Types of Substituent Groups Halogens used as substituent groups. F - fluoro- Cl - chloro- Br - bromo- I - iodo-  

Rules for Naming Branched-chain Hydrocarbons 1.Here is a simple list of rules to follow. Some examples are given at the end of the list. 2.Identify the longest carbon chain. This chain is called the parent chain. 3.Identify all of the substituents (groups appending from the parent chain). 4.Number the carbons of the parent chain from the end that gives the substituents the lowest numbers. When comparing a series of numbers, the series that is the "lowest" is the one which contains the lowest number at the occasion of the first difference. If two or more side chains are in =positions, assign the lowest # to the one which will come first in the name. 5.If the same substituent occurs more than once, the location of each point on which the substituent occurs is given. In addition, the number of times the substituent group occurs is indicated by a prefix (di, tri, tetra, etc.). 6.If there are two or more different substituents they are listed in alphabetical order using the base name (ignore the prefixes). The only prefix which is used when putting the substituents in alphabetical order is iso as in isopropyl or isobutyl. The prefixes sec- and tert- are not used in determining alph order except when compared with each other.

7.If chains of equal length are competing for selection as the parent chain, then the choice goes in series to:
a) the chain which has the greatest number of side chains.
b) the chain whose substituents have the lowest- numbers.
c) the chain having the greatest number of carbon atoms in the smaller side chain.
d)the chain having the least branched side chains. 
 8.A cyclic (ring) hydrocarbon is designated by the prefix cyclo- which appears directly in front of the base name. Count the substituent groups to give the lowest numbers for side-groups. 9.Use hyphens to separate numbers from words, comas to separate numbers. Do not add spaces to separate the parent chain from the substituent name.

Example Branched-Chain Alkanes