Hydrocarbons Aliphatic Series Chains or Branched Chains Kenneth
Hydrocarbons Aliphatic Series Chains or Branched Chains Kenneth E. Schnobrich
What Makes Carbon Special? • Note the electron configuration of carbon in the ground state, 2 -4. • Using Lewis Dot Structures we can examine several arrangements for the electrons Case 1 Case 2 Case 3 Case 4 C C 4 single bonds 2 single bonds & 1 double bond 2 double bonds 1 single Bond & 1 triple bond
Carbon Special cont. • Case #1 - atoms tend to bond in a tetrahedral fashion around carbon. If they are identical atoms the molecule is nonpolar. • Case #2 - atoms tend to bond in a trigonal planar fashion around carbon. These molecules tend to be polar. • Case #3 - atoms tend to bond in a linear fashion around the carbon. If the bonding atoms are identical the molecule will be nonpolar. • Case #4 - atoms tend to bond in a linear fashion around the carbon. These molecules tend to be polar.
The Alkane Series • Members of the Alkane series all have names that end in “ane”. • They are saturated hydrocarbons - all single bonds between carbon atoms. • They are all members of a homologous series - they each differ by a -CH 2 group. • They all follow the general formula Cn. H 2 n+2 • They undergo substitution reactions
iso-Butane 2 methyl Butane C 4 H 10 Methane CH 4 Ethane C 2 H 6 n-Pentane C 5 H 12 Propane C 3 H 8 n-Butane C 4 H 10 iso-Pentane 2 methyl Butane C 5 H 12
Isomers • Notice that in Butane and Pentane the molecular formula is the same but there are different arrangements for the atoms. This defines an isomer - same formula, different arrangement. • Look at Hexane on the next slide
Hexane & Isomers n-Hexane C 6 H 14 2, 3 dimethyl Butane C 6 H 14 2, 2 dimethyl Butane C 6 H 14
Rules for Naming • Locate the longest continuous chain of carbon atoms (that is the base name) • Number the carbons in the longest chain starting from that end to which the attached group (or groups) are closest • If there is more than one of the same attached group you must use a prefix like - di, tri, tetra • Identify the number of the carbon on the longest chain to which the groups are each attached
Let’s Use Hexane Methyl group -CH 3 1 2 4 3 Methyl group -CH 3 - Notice there are four carbons in the longest continuous chain (Butane) -You can # from either end because of the location of the attached “methyl” groups - Since there are two “methyl” groups you must use the prefix “di” (dimethyl) - Notice that one is on carbon 2 and the other on carbon 3 - So the final name would be 2, 3 dimethyl Butane
Next Isomer of Hexane both Methyl groups on carbon #2 Methyl group -CH 3 2 4 1 3 - Notice there are four carbons in the longest continuous chain (Butane) -You must # from the left end because of the location of the two attached “methyl” groups - Since there are two “methyl” groups you must use the prefix “di” (dimethyl) - Notice that both “methyl” groups are on carbon 2 - So the final name would be 2, 2 dimethyl Butane
Isomers • It should be noted that as the number of carbons increases the number of possible isomers increases considerably. • For example, Octane (C 8 H 18), there are 18 possible isomers including a continuous chain of 8 carbons.
The Alkene Series • Members of the Alkene series all have names that end in “ene”. • The are unsaturated hydrocarbons - there is one double bond between two carbon atoms. • They are all members of a homologous series - they differ by a -CH 2 group • They all follow the general formula Cn. H 2 n • They undergo addition reactions
Alkene Series cont. • Since the double bond can appear anywhere in the longest chain you must identify its location by numbering the bond spaces. • Always start from that end of the carbon chain to which the double bond is closest.
1 2 Note the double bond - since there are only two bond spaces the name is simply Propene 2 1 Note the double bond - since there are only two bond spaces the name is simply Propene
The double bond appears in bond position #1 so the compound is named Butene-1 3 2 1 The double bond appears in bond position #2 so the compound is named Butene-2 - it doesn’t matter which end you number from, the double bond appears in the second bond space 2 1 3 Note - as the number of carbons in the chain increases the number of possible double bond locations increases
Alkyne Series • The alkynes are hydrocarbons whose names all end with “yne”. • The alkynes are characterized by a triple bond between two carbon atoms somewhere in the structure. • The alkynes are unsaturated and follow the general formula Cn. H 2 n-2. • Alkynes undergo addition reactions at the triple bond.
Alkyne Series (cont. ) • The first member of the alkyne series is ethyne (commonly called acetylene) and its formula is C 2 H 2. Triple bond • As the carbon chain grows longer (4 or more carbons) it is necessary to locate the triple bond in the name of the compound.
Alkyne Series (cont. ) • Now you must number the bond spaces (between the carbon atoms) starting from that end of the chain to which the triple bond is closest. 2 1 3 3 2 1 4 Triple bond You can tell the triple bond by the Shorter bond distance Butyne-1 or 1 -Butyne Pentyne-2 or 2 -Pentyne
General Comments • Whether it is the alkane, alkene, or alkyne series they are considered homologous series because each member differs by the same –CH 2 grouping (or structure). • In all of the series, the greater the complexity of the structure the higher the boiling point.
General Comments (cont. ) • Alkanes (saturated hydrocarbons) undergo substitution reactions. • Alkenes and Alkynes (unsaturated hydrocarbons) undergo addition reactions. • Organic compounds generally have low melting and boiling points (weak intermolecular attractions).
Aromatic Hydrocarbons • Aromatic hydrocarbons have typical, sometimes unpleasant, odors. • Benzene, the first member of the Benzene series, has a unique ring structure with alternating double bonds. Double bond Just another way of representing Benzene Double bond
Aromtic Hydrocarbons • The second member of the Benzene series is Toluene (foul smelling). -CH 3 • The general formula for the series is Cn. H 2 n-6.
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