Organic ChemistryOrganic Chemistry

Nomenclature: Nomenclature: AlkanesAlkanes

AlkanesAlkanes

• Hydrocarbon chains where all the bonds Hydrocarbon chains where all the bonds between carbons are SINGLE bondsbetween carbons are SINGLE bonds

• Name uses the ending –Name uses the ending –aneane

• Examples: MethExamples: Methaneane, Prop, Propaneane, But, Butaneane, , OctOctaneane, 2-methylpent, 2-methylpentaneane

Summary: IUPAC Rules for Alkane Summary: IUPAC Rules for Alkane NomenclatureNomenclature

 1.1.   Find and name the longest continuous carbon chain.   Find and name the longest continuous carbon chain. This is called the This is called the parent chainparent chain. (Examples: methane, . (Examples: methane, propane, etc.)propane, etc.)

  2.2.   Number the chain consecutively, starting at the end   Number the chain consecutively, starting at the end nearest an attached group (nearest an attached group (substituentsubstituent). ).

  3.3.   Identify and name groups attached to this chain.   Identify and name groups attached to this chain. (Examples: methyl-, bromo-, etc.)(Examples: methyl-, bromo-, etc.)

  4.4.   Designate the location of each substituent group with   Designate the location of each substituent group with the number of the carbon parent chain on which the the number of the carbon parent chain on which the group is attached. Place a dash between numbers and group is attached. Place a dash between numbers and letters. (Example: 3-chloropentane)letters. (Example: 3-chloropentane)

  5.5.   Assemble the name, listing groups in alphabetical   Assemble the name, listing groups in alphabetical order. order.     The prefixes di, tri, tetra etc., used to designate     The prefixes di, tri, tetra etc., used to designate several groups of the same kind, are not considered several groups of the same kind, are not considered when alphabetizing. Place a comma between multiple when alphabetizing. Place a comma between multiple numbers. (Example: 2,3-dichloropropane)numbers. (Example: 2,3-dichloropropane)

Step 1. Find the parent chain.Step 1. Find the parent chain.

• Where is the longest continuous chain of Where is the longest continuous chain of carbons?carbons?

Prefixes for # of CarbonsPrefixes for # of Carbons

11 MethMeth 66 HexHex

22 EthEth 77 HeptHept

33 PropProp 88 OctOct

44 ButBut 99 NonNon

55 PentPent 1010 DecDec

EndingsEndings

• Alkanes (all C-C single bonded parent Alkanes (all C-C single bonded parent chain) end in chain) end in –ane–ane– MethMethaneane CHCH44

– EthEthaneane CC22HH66

– PropPropaneane CC33HH88

• Attached carbon groups (substituents) end Attached carbon groups (substituents) end in in –yl–yl– MethMethylyl CH CH33 - -– EthEthylyl CHCH33CHCH22--– PropPropylyl CH CH33CHCH22CHCH2 2 –  –      3-ethylpentane

Step 2. Number the parent chain.Step 2. Number the parent chain.

• Number the parent chain so that the attached groups are on the lowest numbers

1 2 3 4 5

Methyl is on carbon #2 of the parent chain

5 4 3 2 1

Methyl is on carbon #4 of the parent chain

GREEN is the right way for this one!

1 2

3 7 8

4 5 6

8 7

6 2 1

5 4 3

Groups on 2, 3, and 5

Groups on 4, 6, and 7

1 2 3 4 5 6

7

Groups on 2 and 5

7 6 5 4 3 2 1

Groups on 3 and 6

Step 3. Name the attached groups.Step 3. Name the attached groups.

• Carbon (alkCarbon (alkylyl) groups) groups– MethMethylyl CH CH33 - -– EthEthylyl CHCH33CHCH22--– PropPropylyl CH CH33CHCH22CHCH2 2 ––

• HalogensHalogens– Fluoro (F-)Fluoro (F-)– Chloro (Cl-)Chloro (Cl-)– Bromo (Br-)Bromo (Br-)– Iodo (I-)Iodo (I-)

Step 4. Designate where the group Step 4. Designate where the group is attached to the parent chain.is attached to the parent chain.

• Use the numbers of the parent chain from step 2 to designate the location of the attached groups to the parent chain.

1 2 3 4 5

2-methyl

Step 5. Alphabetize the groups, Step 5. Alphabetize the groups, combine like groups, and assemble.combine like groups, and assemble.

• The prefixes di, tri, tetra The prefixes di, tri, tetra etc., used to designate etc., used to designate several groups of the several groups of the same kindsame kind

• Prefixes are not Prefixes are not considered when considered when alphabetizing (Example: alphabetizing (Example: dimethyl = m for dimethyl = m for alphabetizing)alphabetizing)

• Parent chain goes LASTParent chain goes LAST

1,1,1-trichloro-1-fluoromethane

1,1-dichloro-1,1-difluoromethane

Draw Some Simple AlkanesDraw Some Simple Alkanes

• 2-methylpentane2-methylpentane

• 3-ethylhexane3-ethylhexane

• 2,2-dimethylbutane2,2-dimethylbutane

• 2,3-dimethylbutane2,3-dimethylbutane

Structural FormulasStructural Formulas

• “Lazy” way to write the Hydrogens

• Instead of drawing the bonds, just state how many hydrogens are attached

• NOTE: The bonds are between CARBONS in a parent chain, and not hydrogens!

Structural FormulaLewis Structure

C5H12 pentane(s)

CH3CH2CH2CH2CH3 n-pentane

CH3CHCH2CH3 isopentane

CH3CCH3 neopentane

CH3

CH3

CH3

these are common, or trivial, names where a prefix isused to idicate the structure.

hexanes C6H14 common names

CH3

CH3CH2CH2CH2CH2CH3 CH3CHCH2CH2CH3

n-hexane isohexane

CH3 CH3

CH3CH2CHCH2CH3 CH3CCH2CH3

????? CH3

neohexane

CH3

CH3CHCHCH3

CH3

????

IUPAC nomenclature (Geneva, 1920)

names of radicals (alkyl groups):

CH3- “methyl” CH3Cl methyl chloride

CH3OH methyl alcohol, etc.

CH3CH2- “ethyl”

CH3CH2CH2- “n-propyl” CH3CHCH3 “isopropyl” |

CH3CH2CH2CH2- “n-butyl”

CH3

CH3CH2CHCH3 or CH3CH2CH- “sec-butyl” |

CH3

CH3CHCH2- “isobutyl”

CH3

CH3CCH3 “tert-butyl” |

Alkanes

hexanes C6H14 IUPAC names CH3

CH3CH2CH2CH2CH2CH3 CH3CHCH2CH2CH3

(n-hexane) (isohexane) n-hexane 2-methylpentane CH3 CH3

CH3CH2CHCH2CH3 CH3CCH2CH3

(no common name) CH3

3-methylpentane (neohexane)2,2-dimethylbutane

CH3

CH3CHCHCH3

CH3

(no common name)2,3-dimethylbutane

Alkanes

Physical Properties

Boiling points

Boiling Points of Alkanes

IsomersIsomers

• Straight chain alkanes:Straight chain alkanes: An alkane that An alkane that has all its carbons connected in a row.has all its carbons connected in a row.• Branched chain alkanes:Branched chain alkanes: An alkane An alkane that has a branching connection of that has a branching connection of carbons.carbons.• Isomers: Isomers: Compounds with same Compounds with same molecular formula but different molecular formula but different structures.structures.

Alkane name isomers

CH4 methane 1

C2H6 ethane 1

C3H8 propane 1

C4H10 butanes 2

C5H12 pentanes 3

C6H14 hexanes 5

C7H16 heptanes 9

C8H18 octanes 18

C9H20 nonanes 35

C10H22 decanes 75

…….

C20H42 eicosanes 366,319

each new common name requires a new prefix…

• There is only one possible way that the There is only one possible way that the carbons in methane (CHcarbons in methane (CH44), ethane (C), ethane (C22HH66), ),

and propane (Cand propane (C33HH88) can be arranged.) can be arranged.

• However, carbons in butane (CHowever, carbons in butane (C44HH1010) can ) can be arranged in two ways; four carbons in a be arranged in two ways; four carbons in a row (linear alkane) or a branching row (linear alkane) or a branching (branched alkane). These two structures (branched alkane). These two structures are two isomers for butane.are two isomers for butane.

•Different isomers are completely different Different isomers are completely different compounds. They have different structures, compounds. They have different structures, different physical properties such as melting point different physical properties such as melting point and boiling point, and may have different and boiling point, and may have different physiological properties.physiological properties.

Learning CheckLearning Check

• Draw all possible structural isomers of C5H12

Types of Carbon AtomsTypes of Carbon Atoms

• Primary carbon (1Primary carbon (1oo))

– a carbon bonded to a carbon bonded to

one other carbonone other carbon

• Secondary carbon (2Secondary carbon (2oo))

– a carbon bonded to a carbon bonded to

two other carbonstwo other carbons

• Tertiary carbon (3Tertiary carbon (3oo))

– a carbon bonded to a carbon bonded to

three other carbonsthree other carbons

C

C

C

C

H

H

H

C C

H

HC

C

C

H

C

C

C

C

H

H

H

C C

H

HC

C

C

H

C

C

C

C

H

H

H

C C

H

HC

C

C

H

C

C

C

C

H

H

H

C C

H

HC

C

C

H

AlkanesAlkanes

Example:Example: Name the following compounds: Name the following compounds:

CH3

CH3CH(CH

3)2CH

2CH

2Br

CH3

CH CH CH2

CH CH3

CH2CH

3C

CH

CH3

CH3

CH3

CH3

CH3

C CH2 CH

2Br

CHCH3

CH2CH

3

CH3

CH3

CH CH CH2

CH CH3

CH2CH

3C

CH

CH3

CH3

CH3

CH3

CH3

AlkanesAlkanes

Example: Write the condensed structure Example: Write the condensed structure for the following compounds:for the following compounds:

3,3-dimethylpentane3,3-dimethylpentane

2-methyl-4-sec-butyloctane2-methyl-4-sec-butyloctane

1,2-dichloro-3-methylheptane1,2-dichloro-3-methylheptane

Environmental transformations

• When released in the environment, alkanes don't undergo rapid biodegradation, because they have no functional groups (like hydroxyl or carbonyl) that are needed by most organisms in order to metabolize the compound.

• However, some bacteria can metabolize some alkanes (especially those linear and short), by oxidizing the terminal carbon atom. The product is an alcohol, that could be next oxidized to an aldehyde, and finally to a carboxylic acid. The resulting fatty acid could be metabolized through the fatty acid degradation pathway.

Hazards

• Methane is explosive when mixed with air (1 – 8% CH4). Other lower alkanes can also form explosive mixtures with air. The lighter liquid alkanes are highly flammable, although this risk decreases with the length of the carbon chain. Pentane, hexane, heptane, and octane are classed as dangerous for the environment and harmful. The straight-chain isomer of hexane is a neurotoxin.

• Considerations for detection /risk control:– Methane is lighter than air (possibility of accumulation on roofs)

– Ethane is slightly Heavier than air (possibility of pooling at ground levels / pits)

– Propane is Heavier than air (possibility of pooling at ground levels / pits)

– Butane is Heavier than air (possibility of pooling at ground levels / pits)

Assignment

• Reaction of Alkene.– Reactions with oxygen (combustion

reaction)– Reactions with halogens