1. Hydrocarbons
Chemistry ch 21

2. Objectives Explain the organic compound and organic chemistry
Identify hydrocarbons and the models used to represent them
Distinguish between saturated and unsaturated hydrocarbons
Name alkanes and alkenes by examining their structures.
Draw the structure of an alkane and alkenes when given its name

3. Hydrocarbons
Organic Chemistry – branch of chemistry that deals with carbon compounds
All living organisms have carbon in them
Organic compound is applied to all carbon-containing compounds with the primary exceptions of carbon oxides, carbides, and carbonates, which are considered inorganic
In organic compounds, carbon nearly always shares its electrons and forms four covalent bonds
Carbon atoms are bonded to hydrogen atoms or other elements near carbon on the periodic table.
Carbon atoms also bond to other carbon atoms and form long chains

4. Hydrocarbons
The simplest organic compounds are hydrocarbons, which consist of only the elements carbon and hydrogen
There are thousands of hydrocarbons
Carbon atoms bond to each other by single, double, and triple bonds Saturated hydrocarbons contain only single bonds.
Contain the maximum number of hydrogens
Unsaturated hydrocarbons contain at least one double or triple bond.

5. Condensed Structural Formula
2 Types of Hydrocarbons
1. Aliphatic compounds – hydrocarbon compounds that do not contain rings
Made of chain of carbons
CH3 – CH2 – CH3
C3H8
Condensed Structural Formula
Complete Structural Formula
Molecular Formula
Types of Aliphatic compounds
Alkanes – contain only single bonds between carbons
Alkenes – contain a double bond between carbons
Alkynes – contain a triple bond between carbons

6. Types of Hydrocarbons
Cyclic hydrocarbons –compounds that contain hydrocarbon rings
Double bond
Single bond
Cyclic hydrocarbons with only single bonds are called cycloalkanes

7. Aliphatic Compounds (chains)
Alkanes – Simplest hydrocarbons that contain only single covalent bonds, have maximum number of hydrogens (saturated)
CH4, methane, is simplest of alkanes
Straight-chain alkanes – contain a number of carbon atoms and form a chain
CH3 – CH2 – CH2 – CH2 – CH3 Pentane
Homologous series – constant increment of change in molecular structure
Example: Alkanes increase by CH2

8. How to draw and name Straight-chained alkanes
Draw the number of carbons as indicated by the root name
Table 21.2, LEARN IT!!
Names of alkanes always end in -ane
Fill in hydrogen's to complete 4 carbon bonds
Given: Heptane
Step 1: Hept = 7
C – C – C – C – C – C – C
Step 2: Fill in hydrogen’s
C – C – C – C – C – C – C

9. How to draw and name Straight-chained alkanes
Given: CH3CH2CH2CH2CH3
Step 1: Count the carbons
5 carbons = Pent
Step 2: add - ane
Pentane

10. Branched-chain Alkanes
Order and arrangement of atoms in organic compounds determine their identities
When naming branched chain alkanes, the longest continuous chain of carbon atoms is called the Parent Chain
All side branches are known as Substituent groups

11. Branched-chain Alkanes
Alkyl group (al kill) – a hydrogen substituent
Common alkyl groups are:
Methyl CH3 -
Ethyl CH3CH2 –
Propyl CH3CH2CH2 –
Naming – remove (-ane) ending and add (-yl) ending

12. Naming Branched-chain Alkanes
Use prefixes if a substituent appears more than once in the structure
Example: di-, tri-, tetra-, etc…..
List the names of the alkyl subsituents in alphabetical order
Ignore di-, tri-, etc…
Proper punctuation
Commas used to separate numbers
Hyphens used to separate numbers and words
Entire name is written without any spaces
CH3
Find the longest chain of carbons
This is the parent chain
Number the carbons in the parent chain sequence
Start at the end that gives the attached groups the smallest #
Add numbers to the names of the substituent groups to indentify their positions on the chain
The numbers become prefixes to the name of the parent alkane |
CH3–CH2–CH2–CH–CH2–CH3

13. Naming Branched-chain Alkanes|
CH2
CH3 – CH2 – C – CH2 – CH2 – CH2 – CH3
4 – ethyl – 4 - methyloctane
CH3 – CH2 – C – CH3 |
CH3
CH2
3,3 - dimethylhexane

14. Naming Branched-chain Alkanes|
CH2
CH2 – CH2 – CH – CH2 – CH2
4 - ethylheptane
CH3 – CH2 – CH2 - C – CH2 - CH3 |
CH3
CH2
3 – ethyl – 3 - methylhexane

15. Writing Branched-chain Alkanes
2, 3, 4 - Trimethyloctane
Write out parent chain
Number from left to right
Add in any substituents
Add in hydrogen’s to complete 4 carbon bonds
C – C – C – C – C - C – C – C

16. Writing Branched-chain Alkanes
4 - propyloctane
CH2
CH3 |
CH3 – CH2 – CH2 – CH – CH2 – CH2 -CH2 – CH3
CH3 |
CH3 – CH – CH - CH2 – CH2 – CH3
CH2
3 – ethyl – 2 - methylhexane

17. Aliphatic compounds
Alkenes – hydrocarbons containing carbon-carbon double bonds
Alkenes do not have the maximum number of hydrogen’s due to the double bonds
Unsaturated hydrocarbon
Naming Alkenes
Find the longest chain in molecule that contains double bond
This is the parent chain
Chain is numbered so that double bond gets the lowest number possible
Root name used, add –ene ending
Substituents are named and numbered same way as alkanes

18. Naming Alkenes CH2 CH = 3 – propyl – 1 - heptene| =
CH3 – CH2 – CH2 – CH2 – CH – CH2 – CH2 – CH3
3 – propyl – 1 - heptene
1 - Butene
CH2 = CH – CH2 - CH3

19. Aliphatic compounds continued
Alkynes – hydrocarbons containing carbon-carbon triple bonds
Unsaturated compounds
Not plentiful in nature
Naming Alkynes
Same pattern as alkenes
If compound contains double & triple bonds
Double bond take precedence in numbering
Root name plus ending in -yne

20. Isomers
Isomers are two or more compounds that have the same molecular formula (chemical formula) but different molecular structures
The structure of a substance determines the properties of the hydrocarbon
There are two main classes of isomers:
Structural isomers have the same chemical formula but their atoms are bonded in different orders
Stereoisomers are the atoms are bonded in the same order but are arranged differently in space
Example: C5H12

21. Structural Isomers Structural isomers
Same number of atoms, different arrangement
Pentane C5H12 has 3 isomers:

22. Stereoisomers
Stereoisomers are isomers in which all atoms are bonded in the same order but are arranged differently in space
Types of Stereoisomers
Optical isomers – have same physical and chemical properties, except in chemical reactions where chirality is important (medical drugs)
Chirality – right or left handedness of molecule
Geometric isomers – different arrangements of groups of around a double bond

23. Stereoisomers
Geometric isomers result from different arrangements of groups around a double bond
Geometric isomers have different physical and chemical properties
Cis means on the same side, and trans means across from

24. Properties of Aliphatic hydrocarbons
STRUCTURE AFFECTS MOLECULAR PROPERTIES
Alkanes are not polar and are good solvents for other nonpolar molecules
Alkanes have low reactivity because they are nonpolar and have no charge, and because they have strong single bonds between carbon atoms.
Alkenes are nonpolar and have low solubility in water. Alkenes are more reactive than alkanes because the double bond increases electron density between the two carbon atoms, providing a good site for chemical reactivity
Alkynes have physical and chemical properties similar to alkenes but are generally more reactive because the triple bonds cause even larger electron densities than double bonds

25. Cyclic hydrocarbons Cyclic hydrocarbon - contains a hydrocarbon ring
Cycloalkanes - Cyclic hydrocarbons with only single bonds
Aromatic hydrocarbons (Arenes) are unusually stable compounds with ring structures in which electrons are shared by many atoms (double bonds!)

26. Naming Cycloalkanes The ring is always considered the parent chain
Cyclopropane
Cyclobutane
Cyclopentane
Cyclohexane
The ring is always considered the parent chain
Cyclic hydrocarbons has the prefix "cyclo-”
Number the substituents of the chain so that the sum of the numbers are the lowest possible.
The name is assembled, substituents in alphabetical order and giving each group (if there are two or more) a location number.
The prefixes di, tri, tetra etc., are not considered when alphabetizing.
1+3=4
NOT
1+5=6

27. Benzene
The configuration of six carbon atoms in aromatic compounds is known as a benzene ring
Unsaturated cyclic hydrocarbons
Aromatic was originally used because many benzene related compounds were found in pleasant smelling oils that came from plants and plant parts
The double bonds in benzene are not fixed, but rather the electrons are delocalized and shared among all six carbon atoms
Resonance occurs in Benzene
When 2 or more valid structures can be drawn for a molecule
Use an inscribed circle to represent resonance

28. Key concepts
Organic compounds contain the element carbon, which is able to form straight chains and branched chains.
Hydrocarbons are organic substances composed of carbon and hydrogen
The major sources of hydrocarbons are petroleum and natural gas.
Petroleum can be separated into components by the process of fractional distillation
Alkanes contain only single bonds between carbon atoms.
Alkanes and other organic compounds are best represented by structural formulas and can be named using systematic rules determined by the International Union of Pure and Applied Chemistry (IUPAC)
Alkanes that contain hydrocarbon rings are called cyclic alkanes.