Organic Chemistry

Chemistry of Carbon Compounds(except oxides, carbides, &

carbonates)

Why so many C compounds?

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

• Bonds are covalentcovalent.

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.

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.

Properties of Covalent Substances

(also called molecularmolecular 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

Chemical FormulasChemical Formulas

• show kind & number of atoms.

CH2Cl2

CH4

CH3OH

CH3Cl

Structural FormulasStructural 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

aren’t totally realistic. H

H–C–H H

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).

Shape

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

• 109.5 apart.

Vocabulary Interlude

• SaturatedSaturated: organic compounds containing only SSingle bonds.

• UnsaturatedUnsaturated: organic compounds containing one or more double or triple bonds.

Vocabulary

• HydrocarbonsHydrocarbons: organic compounds containing only C and H.

• Homologous SeriesHomologous 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.

Homologous Series

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

CondensedCondensed Structural Formula 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

H–CC–CC–CC–H

H H H

Becomes CCH3CCH2CCH3

Alkanes• Homologous series of saturated hydrocarbons.• Release energy when burned.

CH4 H H–C–H

H

C2H6 H HH–C–C–H H H

• C2H6 is also written CH3CH3

Above: 3 representations of CH4. Below: Ball and stick model of ethane.

Space-filling model

Alkanes or CnH2n+2

• C3H8

H H H

H–C–C–C–H

H H H

CH3CH2CH3

Chemical Formula

Structural Formula

Condensed Structural Formula

Ball & stick model of propane.

Bond angles = 109.

4th straight-chain alkane

C4H10

H H H H

H–C–C–C–C–H

H H H H

Or CH3CH2CH2CH3

Ball and Stick model of butane.

Alkanes: base unit

CH4

CH3CH3 or C2H6

CH3CH2CH3 or C3H8

CH3CH2CH2CH3 or C4H10

CH3CH2CH2CH2CH3 or C5H12

Difference between each is CHCH22

Naming straight-chain Alkanes

• Name describes molecule so you can draw it.

• All alkaneanes have the suffix –aneane.

• The prefix depends on the number of C’s.

Prefix # of C atoms

Meth 1

Eth 2

Prop 3

But 4

Pent 5

Hex 6

Hept 7

Oct 8

Non 9

Dec 10

Formula Name

CH4 Meth + aneMeth + ane

C2H6

C3H8

C4H10

C5H12

EthaneEthane

PropanePropane

ButaneButane

PentanePentane

Properties of Alkanes

• Change systematically with number of C’s

• As the number of C’s increases, the boiling point increases.– The molecules get heavier & harder to change

into the gas phase.

Properties of Alkanes

• Low Reactivity

• Except readily undergo combustion – fuels

• Nonpolar – Don’t dissolve well in water.

• Low melting pts & boiling pts.

• (M.P. & B.P. increase with molecular mass)

• High vapor pressures

A. Low melting point

B. High melting point

C. Soluble in polar solvents

D. Insoluble in nonpolar solvents

Which property is generally characteristic of an organic compound?

Correct response = ACorrect response = A

A. CH4

B. C2H6

C. C3H8

D. C4H10

Which of the following compounds has the highest boiling point?

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

Branched-chain alkanesBranched-chain alkanes

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

H

H–C–H

H H

H–C–C–C–H

H H H

Branched alkane.Can’t link all the C’s without lifting pencil off the paper.

Methyl propane

IsomersIsomers

• 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.

Isomers

• Different structures, different Different structures, different properties.properties.

• Isomers have different chemical and physical properties.

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!

These diagrams represent the same molecule.

Represents bond to H

These diagrams represent the same molecule.

Represents bond to H

These diagrams represent the same molecule.

Represents bond to H

Two different molecules!

Represents bond to H

Naming Branched-Chain Alkanes

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

Naming branched-chain alkanes• Find the longest continuous chainlongest continuous chain or backbone of C atoms.

(Bends don’t count!)• The base namebase name is derived from the number of C’s in the

longest chain.• BranchesBranches are named inin the prefixprefix. Branches are also named

by the number of C atoms. The “branchbranch” part of the name ends in “yl.”ends in “yl.”

• The location of the branch is shown by assignassigning numbers to numbers to the C’s in the backbonethe C’s 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.

H

H–C–H

H H

H–C–C–C–H

H H H

Branch has 1 carbon – methylmethyl.

Branch has to be at C-2.(Only give the number if necessary.)

Methyl propaneMethyl propane

C4H10

CH3CH(CH3)CH3

Longest continuous chain has 3 carbon atoms – propanepropane.

HH–C–H

H–C–H H H HH–C–C–C–C–H H H H H–C–H H

Longest continuous chain has 6 carbon atoms. It’s a hexanehexane.

Branch is 1 carbon long – methyl methyl.

Branch is located at C-22.

2-methyl hexane2-methyl hexane

C7H16

CH3CH(CH3)CH2CH2CH2CH3

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.

H

H – C – H

H H HH – C – C – C – C – H H H H–C–H H–C–H H H

Longest continuous chain has 6 carbon atoms: hexaneBranch is 1 carbon long: methylBranch is located at C-3

3-methyl hexane

C7H16

CH3CH2CH2CH(CH3)CH2CH3

CH3(CH2)2CH(CH3)CH2CH3

Alkenes

• Another homologous series of hydrocarbons hydrocarbons.

• Each member contains oneone double covalent bond between C atoms.

So alkenes are unsaturatedunsaturated.

• General formula = CnH2n

Naming Alkenes

• Names: # of C’s in parent chain gives prefix. Suffix = -ene.

1st member is C2H4, ethene.

H HH HCC=C=C

H H H H

Alkenes with 4 or more C’s

• Number C atoms.

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

Naming Alkenes• Number C atoms in backbone. Give double

bond the lowest possible number.

H H H C=C–C–C–HH H H H

C4H8

CH2CHCH2CH3

H H H HH–C–C=C–C–H H H

C4H8

CH3CHCHCH3

1-butene 2-butene

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 #.

Properties of Alkenes

• Nonpolar – low solubility in H2O

• Fairly low M.P. & B.P.

• More reactive than alkanes – double bond = site of reactivity.

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

Naming Alkynes

• Name: Prefix depends on # of C’s. Suffix = -yne.

• If necessary, number the 1st carbon atom at which the triple bond occurs.

H–CC–H C2H2 ethyne CHCH

HH–CC–C–H H

H HH–CC–C–C–H H H

H HH–C–CC–C–H H H

C3H4 propyne CHCCH3

C4H6 1-butyne CHCCH2CH3

C4H6 2-butyne CH3CCCH3

3 Homologous Series of HC’s

Name of Series General Formula Ending

Alkanes CnH2n+2 -ane

Alkenes CnH2n -ene

Alkynes CnH2n-2 -yne

A. C2H2

B. C2H4

C. C6H6

D. C6H14

Which compound belongs to the alkene series?

Correct answer = B. Alkenes follow Correct answer = B. Alkenes follow the format Cthe format CnnHH2n2n. A & C are C. A & C are CnnHHnn. .

D is CD is CnnHH2n+22n+2..

A. C2H2, C2H4, C2H6

B. C2H4, C3H4, C4H8

C. C2H4, C2H6, C3H6

D. C2H4, C3H6, C4H8

In which group could the hydrocarbons all belong to the same homologous series?

Correct answer = D. Members of a homologous series Correct answer = D. Members of a homologous series all have the same relationship between the atoms. all have the same relationship between the atoms. Every compound in set D fits the formula CEvery compound in set D fits the formula CnnHH2n2n..

A. Ethene

B. Ethyne

C. Propene

D. Propane

Which of the following is a saturated hydrocarbon?

Correct answer = D. The alkanes are Correct answer = D. The alkanes are saturated.saturated.