Organic Chemistry

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Organic Chemistry

• Chemistry of Carbon Compounds
• (except oxides, carbides, carbonates)

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Why so many C compounds?

• Carbon atoms can bond with other carbon atoms in
  chains, rings, and networks.
• Bonds are covalent.

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Lewis Diagram of C

• C
• Carbon has 4 unpaired electrons.
• It can form 4 covalent bonds.
• Note C can form only 3 bonds to any other
  single C atom.

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Bonding Capacity of H, O, etc.

• H can form only 1 bond.
• O and S like to form 2 bonds.
• The halogens (F, Cl, Br, I) form only 1 bond.
• N and P form 3 bonds.

Memory Jogger
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Properties of Covalent Substances

• (also called molecular substances)
• Low melting boiling points
• Poor conductors of heat electricity
• May be soft or brittle
• Generally nonpolar van der Waals forces
• Tend to dissolve in nonpolar solvents
• React more slowly than ionic compounds

Memory Jogger
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Chemical Formulas

• show kind number of atoms.
• CH2Cl2

Memory Jogger
CH3OH
CH4
CH3Cl
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Structural Formulas

• Show kind number of atoms.
• Also show bonding patterns and approximate shapes
  of molecules.
• 2-D rep of 3-D object so structural formulas
  arent totally realistic.
• H
• HCH
• H

Memory Jogger
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Structural Formulas

• A single line represents one pair of electrons
  (a single bond).
• A double line represents two pairs of electrons
  (a double bond).
• ? A triple line represents three pairs of
  electrons (a triple bond).

Memory Jogger
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Shape

• The 4 unpaired electrons around the C atom are
  located at the corners of a tetrahedron.
• 109.5? apart.

Memory Jogger
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Vocabulary Interlude

• Saturated organic compounds containing only
  Single bonds.
• Unsaturated organic compounds containing one or
  more double or triple bonds.

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Vocabulary

• Hydrocarbons organic compounds containing only
  C and H.
• Homologous Series a group of compounds with
  related structures and properties. Each member
  of the series differs from the one before it by
  the same additional unit.

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Homologous Series

• The molecules have a fixed, numerical
  relationship among the numbers of atoms.

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Condensed Structural Formula

• Shows kind number of atoms
• Shows some structural information, but not all
  the details. Fits on 1 line of type.
• H H H
• HCCCH
• H H H
• Becomes CH3CH2CH3

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Alkanes

• Homologous series of saturated hydrocarbons.
• Release energy when burned.
• CH4 H
• HCH
• H
• C2H6 H H
• HCCH
• H H
• C2H6 is also written CH3CH3

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Space-filling model
Above 3 representations of CH4. Below Ball
and stick model of ethane.
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Alkanes or CnH2n2

• C3H8
• H H H
• HCCCH
• H H H
• CH3CH2CH3

Homologous Series
Chemical Formula
Structural Formula
Condensed Structural Formula
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Ball stick model of propane. Bond angles
109?.
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4th straight-chain alkane

• C4H10
• H H H H
• HCCCCH
• H H H H
• Or CH3CH2CH2CH3

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Ball and Stick model of butane.
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Alkanes base unit

• CH4
• CH3CH3 or C2H6
• CH3CH2CH3 or C3H8
• CH3CH2CH2CH3 or C4H10
• CH3CH2CH2CH2CH3 or C5H12
• Difference between each is CH2

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Naming straight-chain Alkanes

• Name describes molecule so you can draw it.
• All alkanes have the suffix ane.
• The prefix depends on the number of Cs.

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Table P
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Ethane
Propane
Butane
Pentane
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Properties of Alkanes

• Change systematically with number of Cs
• As the number of Cs increases, the boiling point
  increases.
• The molecules get heavier harder to change into
  the gas phase.

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Properties of Alkanes

• Low Reactivity
• Except readily undergo combustion fuels
• Nonpolar Dont dissolve well in water.
• Low melting pts boiling pts.
• (M.P. B.P. increase with molecular mass)
• High vapor pressures

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Which property is generally characteristic of an
organic compound?

• Low melting point
• High melting point
• Soluble in polar solvents
• Insoluble in nonpolar solvents

Correct response A
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Which of the following compounds has the highest
boiling point?

• CH4
• C2H6
• C3H8
• C4H10

Correct answer D. In nonpolar covalent
compounds, the boiling point depends on the
strength of the van der Waals interactions. The
van der Waals forces increase as the size of the
molecule increases. (Bigger molecule, bigger
electron cloud.)
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Branched-chain alkanes

• Beginning with butane, C4H10, there is more than
  1 way to arrange the atoms.
• H
• HCH
• H H
• HCCCH
• H H H

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Branched alkane. Cant link all the Cs without
lifting pencil off the paper.
Methyl propane
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Isomers

• Compounds with the same molecular formula but
  different structural arrangement.
• The more C atoms there are in the formula, the
  more isomers there will be. ? More possible ways
  to arrange them.

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Isomers

• Different structures, different properties.
• Isomers have different chemical and physical
  properties.

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A note about isomers ---

• If you are comparing 2 structural formulas you
  can superimpose them, they are not isomers they
  are the same molecule!
• If you can rotate or flip one of the structural
  formulas then superimpose it on the other one,
  they are not isomers they are the same molecule!

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These diagrams represent the same molecule.
Represents bond to H
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These diagrams represent the same molecule.
Represents bond to H
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These diagrams represent the same molecule.
Represents bond to H
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Two different molecules!
Represents bond to H
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Naming Branched-Chain Alkanes

• The goal of the name is to describe the molecule
  so you can draw it.

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Naming branched-chain alkanes

• Find the longest continuous chain or backbone of
  C atoms. (Bends dont count!)
• The base name is derived from the number of Cs
  in the longest chain.
• Branches are named in the prefix. Branches are
  also named by the number of C atoms. The
  branch part of the name ends in yl.
• The location of the branch is shown by assigning
  numbers to the Cs in the backbone. Number from
  the end that gives the lowest number for the
  branch.
• There may be more than 1 of the same type of
  branch. Use di, tri, etc.

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Branch has 1 carbon methyl. Branch has to be
at C-2. (Only give the number if
necessary.) Methyl propane C4H10
CH3CH(CH3)CH3
H HCH H H HCCCH H H H
Longest continuous chain has 3 carbon atoms
propane.
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Longest continuous chain has 6 carbon atoms.
Its a hexane. Branch is 1 carbon long
methyl. Branch is located at C-2. 2-methyl
hexane C7H16 CH3CH(CH3)CH2CH2CH2CH3
H HCH HCH H H H HCCCCH
H H H HCH H
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A note about branches

• If you have several branches with the same of C
  atoms, you can condense the name a little.
• 2-methyl 3-methyl pentane becomes 2,3-dimethyl
  pentane.
• The of numbers must match the of branches.

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Longest continuous chain has 6 carbon atoms
hexane Branch is 1 carbon long methyl Branch is
located at C-3 3-methyl hexane C7H16 CH3CH2CH2C
H(CH3)CH2CH3 CH3(CH2)2CH(CH3)CH2CH3
H H C H H H H H
C C C C H H H
HCH HCH H H
Bends Don't Count!
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Alkenes

• Another homologous series of hydrocarbons.
• Each member contains one double covalent bond
  between C atoms. ?So alkenes are unsaturated.
• General formula CnH2n

Homologous Series
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Naming Alkenes

• Names of Cs in parent chain gives prefix.
  Suffix -ene.

1st member is C2H4, ethene. H H CC H
H
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Alkenes with 4 or more Cs

• Number C atoms.
• Use lowest possible to specify location of 1st
  C in double bond.

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Naming Alkenes

• Number C atoms in backbone. Give double bond the
  lowest possible number.

1-butene
2-butene
H H H CCCCH H H H H
H H H H HCCCCH H H
C4H8 CH2CHCH2CH3
C4H8 CH3CHCHCH3
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Naming Branched-Chain Alkenes

• Parent chain longest chain that contains the
  double bond.
• Also, position of double bond, not branches,
  determines numbering of backbone.
• Give 1st C in bond lowest possible .

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Properties of Alkenes

• Nonpolar low solubility in H2O
• Fairly low M.P. B.P.
• More reactive than alkanes double bond site
  of reactivity.

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Alkynes

• Homologous series of unsaturated hydrocarbons
  that contain one triple bond.
• Each member contains one triple carbon-carbon
  bond.
• Alkynes are unsaturated.
• General formula CnH2n-2

Homologous Series
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Naming Alkynes

• Name Prefix depends on of Cs. Suffix
  -yne.
• If necessary, number the 1st carbon atom at which
  the triple bond occurs.

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HC?CH C2H2 ethyne CHCH
H HC?CCH
H
propyne
C3H4
CHCCH3
H H HC?CCCH
H H
1-butyne
C4H6
CHCCH2CH3
H H HCC?CCH
H H
C4H6
2-butyne
CH3CCCH3
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3 Homologous Series of HCs
Table Q
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Which compound belongs to the alkene series?

• C2H2
• C2H4
• C6H6
• C6H14

Correct answer B. Alkenes follow the format
CnH2n. A C are CnHn. D is CnH2n2.
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In which group could the hydrocarbons all belong
to the same homologous series?

• C2H2, C2H4, C2H6
• C2H4, C3H4, C4H8
• C2H4, C2H6, C3H6
• C2H4, C3H6, C4H8

Correct answer D. Members of a homologous
series all have the same relationship between the
atoms. Every compound in set D fits the formula
CnH2n.
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Which of the following is a saturated hydrocarbon?

• Ethene
• Ethyne
• Propene
• Propane

Correct answer D. The alkanes are saturated.