hydrocarbons the basis for organic chemistry. organic compounds contain c bonded to other elements,...

Hydrocarbons

The basis for organic chemistry

Organic Compounds• Contain C bonded to other elements,

commonly H, O, N, S, and halogens

• Carbon – Can form many different compounds due to its

hybrid orbitals– Has intermediate electonegativity, so its most

likely to form molecular compounds (Recall: molecular compounds have diverse properties)

– Can make single, double, and triple bonds– Can form isomers (same molecular formula but

different arrangement of atoms)

Types of Hydrocarbons• Saturated: Contain the maximum number of

hydrogens, single bonds between all carbons

• Unsaturated: Contain 1+ double or triple bonds

• Aliphathic Carbons are arranged in chains

• Cyclic: Carbons are arranged in rings

• Aromatic: Contain a benzene ring

Types of Hydrocarbons

Types of Hydrocarbons

Name Definition General Formula

Alkane Hydrocarbon with only single bonds between

carbon atoms. C2H2n+2

Alkene Hydrocarbon with at

least one double bond. C2H2n

Alkyne Hydrocarbon with at least one triple bond.

C2H2n-2

Naming Alkanes

Based off the number of C atoms in the longest chain

1. Count the number of C’s in the longest chain

2. Determine the appropriate root

3. Add the suffix “ane”

Hydrocarbon Root Names# of Carbons Root Name

1 meth-

2 eth-

3 prop-

4 but-

5 pent-

6 hex-

7 hept-

8 oct-

9 non-

10 dec-

Structural ShorthandStructural Shorthand

H

HH

H

HH

H

H

HH

Explicit hydrogens (those required to complete carbon’s valence) are usually left off of drawings of hydrocarbons

CH3

CH3

Line intersections represent carbon atoms

C1 C1C2 C2

C3 C3C4 C4

Cyclic AlkanesCyclic AlkanesCyclopropane, C3H6

Remember, explicit hydrogens are left out

Cyclobutane, C4H8

Cyclopentane, C5H10

Cyclohexane, C6H12

Cycloheptane, C7H14

Rules for Naming Alkanes Rules for Naming Alkanes (Nomenclature)(Nomenclature)

For a branched hydrocarbon, the longest continuous chain of carbon atoms gives the root name for the hydrocarbon

CH3

CH3

CH3

12 3

4

44 carbon chain = butane carbon chain = butane

Naming Branched Alkanes

Based off the number of C atoms in the longest chain

1. Count the number of C’s in the longest chain

2. Determine the appropriate root

3. Use the numbered C’s to give the branches a position number add “yl” suffix

4. Add the suffix “ane”

Naming Branched Alkanes

Important Rules:1. Start numbering from the end that will give you

the lowest number of branches

2. If there is more than one type of branch, name the branches in alphabetical order

3. If there is more than two of the same type of branch, give the branch a position number and prefixes “di”, “tri” “tetra” etc.

4. Put commas between numbers and hyphens between numbers and letters

Rules for Naming Alkanes Rules for Naming Alkanes (Nomenclature)(Nomenclature)

When alkane groups appear as substituents, theyare named by dropping the -ane and adding -yl.

CH3

CH3

CH3

—CH3 Methyl

—CH2CH3 Ethyl

—CH2CH2CH3 Propyl—CH2CH2CH2CH3 Butyl

Methyl

Rules for Naming Alkanes Rules for Naming Alkanes (Nomenclature)(Nomenclature)

The positions of substituent groups are specifiedby numbering the longest chain of carbon atoms sequentially, starting at the end closest to the branching.

CH3

CH3

CH3

Methyl

12 3

4

Rules for Naming Alkanes Rules for Naming Alkanes (Nomenclature)(Nomenclature)

The location and name of each substituent arefollowed by the root alkane name. The substituentsare listed in alphabetical order (irrespective of anyprefix), and the prefixes di-, tri-, etc. are used toindicate multiple identical substituents.

CH3

CH3

CH3

Methyl

12 3

4 Name:2-methylbutane

Nomenclature PracticeNomenclature Practice

CH3 CH3

CH3

CH3

Cl

Name this compound

Step #1: For a branched hydrocarbon, the longest continuous chain of carbon atoms gives the root name for the hydrocarbon

152 43

9

6

87

9 carbons = nonane

Nomenclature PracticeNomenclature PracticeName this compound

CH3 CH3

CH3

CH3

Cl

152 43

9

6

87

9 carbons = nonane

Step #2: When alkane groups appear as substituents, they are named by dropping the -ane and adding -yl.

CH3 = methyl

chlorine = chloro

Nomenclature PracticeNomenclature PracticeName this compound

CH3 CH3

CH3

CH3

Cl

152 43

9

6

87

9 carbons = nonane

CH3 = methyl

chlorine = chloro

Step #3: The positions of substituent groups are specified by numbering the longest chain of carbon atoms sequentially, starting at the end closest to the branching.

1 9 NOT 9 1

Nomenclature PracticeNomenclature PracticeName this compound

CH3 CH3

CH3

CH3

Cl

152 43

9

6

87

9 carbons = nonane

CH3 = methyl

chlorine = chloro

Step #4: The location and name of each substituent are followed by the root alkane name. The substituents are listed in alphabetical order (irrespective of any prefix), and the prefixes di-, tri-, etc. are used to indicate multiple identical substituents.

2-chloro-3,6-dimethylnonane

Naming Alkenes & Alkynes1. Count the number of C’s in the longest chain

containing the double/triple bond.• This is the parent chain, determine the root• Number the parent chain so that the double/triple bond has

the lowest possible position number

2. Identify the position numbers of branches• Same rules as before

3. Write the branches in alphabetical order4. Write the root, including a prefix that identifies the

position of the double/triple bond• Add the prefix “cyclo” if its cyclic

5. Add the suffix “ene” or “yne”

Naming Alkenes & Alkynes

Naming Cyclic Hydrocarbons

• 1. Number the carbons in the ring, in either direction, so that the multiple bond is between the two lowest numbers, and the branches get the lowest possible position numbers.

• 2. Identify branches.. Prefixes are the same di, tri, prop etc. and are written alphabetically.

• 3. The root is –cyclo- plus the name for the number of carbon atoms in the ring.

• 4. The suffix is –ane for cycloalkanes –ene for cycloalkenes and –yne for cycloalkynes.

Naming Cyclic Hydrocarbons

Naming Aromatics1. Same rules2. If benzene is the parent chain “benzene” suffix3. If benzene is a branch group “phenyl”

Naming Aromatic Hydrocarbons

Properties of Hydrocarbons

• Made up of mostly C and H

• Relatively nonpolar– Low solubility in polar solvents (e.g. water)– Good solvents for other nonpolar molecules

• Mostly london-dispersion forces (weak)– Low boiling and melting points

Reactivity of Hydrocarbons

• Alkanes are generally less reactive than alkenes or alkynes

• Aromatic compounds are more reactive than alkanes, but less reactive than alkenes and alkynes.

Alkanes < aromatics < alkenes < alkynes

Reactions of Hydrocarbons

Combustion:– Hydrocarbons burn readily in air to produce

carbon dioxide and water.

Incomplete Combustion:– Produces carbon and poisonous carbon

monoxide.

C3H8(g) + 5 O2(g) --> 3CO2(g) + H2O(g)

C3H8(g) + 7/2 O2(g) --> C(s) + CO(g) CO2(g) + 4 H2O(g)

Reactions of Alkanes

• Single bonds between carbon atoms are difficult to break. (This is why alkanes are relatively unreactive)

• Can undergo combustion reactions and substitution reactions

Reactions of AlkanesSubstitution Reactions:• Hydrogen atoms may be substituted by a halogen.

• The product is a halogenated alkane (alkyl halides)

Reactions of Alkenes and Alkynes

Addition Reactions:• Reactions in which a molecule is added to a double

or triple bond.• No loss of hydrogen atoms from the hydrocarbon

Types of Addition reactions

Hydrohalogenation

Hydration

Markovnikov’s Rule• “The rich get richer”• When a hydrogen halide is added to an alkene or alkyne,

the hydrogen atom bonds to the carbon atom that already has more hydrogen atoms.

Carbon 1 has 2 H’s Carbon 2 has 1 H

Benzene Ring

• Does not act as 3 single bonds and 3 double bonds

• It’s 6 identical bonds of intermediate length

• Due to hybridization (delocalized, shared electrons)

Reactions of Aromatic Hydrocarbons

• Less reactive than alkenes and do not undergo addition reactions unless under conditions of extreme temperature or pressure

• Do undergo substitution reactions (more reactive than alkanes)