organic chemistry: structure of organic compounds

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Organic Chemistry I

University of Lincoln presentation

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C is a small atom It forms single, double, and triple bondsIt is intermediate in electronegativity (2.5)It forms strong covalent bonds with C, H, O, N, S and some metals

What’s so important about Carbon Chemistry?>7 or 10 or 30! million Organic Compounds (depends on the source) 1.5 million Inorganic Compounds

Lubricants, Cosmetics, Fragrances, Pigments, Dyes, Inks, Adhesives, Explosives, Detergents, Surfactants, Emulsifiers, Coolants, Photographic agents, Forensic chemicals, Plastics, Drugs, ….

And most important!! Is the base of the Chemistry of Life

Organic chemistry



C H

H

H

H

HH

H

H Cx

x

xx

Ne

Methane Neon

Stable Octet required

Covalent bonding – Atoms share electrons

Carbon has 4 valence electrons

Methane



Problem

bonding by 2s and 2p atomic orbitals would give bond angles of approximately 90°.

Instead we observe bond angles of approximately 109.5°, 120°, and 180°

Solution

hybridization of atomic orbitals2nd row elements use sp3, sp2, and sp hybrid orbitals for bonding



2s 2py 2px 2pz 4 x sp3

+++

C(6) – 1s2, 2s2, 2px1, 2py

1, 2pz0

C(6) – 1s2, 2s1, 2px1, 2py

1, 2pz1

Lowest energy state

Excited state

4 sp3



(L. Pauling)“The combination of two or more atomic orbitals forms a new set of atomic orbitals, called hybrid orbitals”

We deal with three types of hybrid orbitals

sp3sp3 (one s orbital + three p orbitals)sp2sp2 (one s orbital + two p orbitals)spsp (one s orbital + one p orbital)

Overlap of hybrid orbitals can form two types of bonds depending on the geometry of overlap σσ bonds bonds are formed by “direct” overlap

ππ bonds bonds are formed by “parallel” overlap

Hybridization of orbitals



– each sp3 hybrid orbital has two lobes of unequal size

– the sign of the wave function is positive in one lobe, negative in the other, and zero at the nucleus

– the four sp3 hybrid orbitals are directed toward the corners of a regular tetrahedron at angles of 109.5°

sp3 Hybrid Orbitals

H

H HH

109.5o

An sp3

orbitalFour tetrahedral sp3 orbitals



Methane is Tetrahedral

H

H HH

HH

H

H109.5oSigma bonds formed by overlap of sp3 and 1s orbitals

Methane

Sp3 hybridized carbon 4 equivalent C-H bonds (s-bonds)



sp sp Hybrid Orbitals Hybrid Orbitals22

– the axes of the three sp2 hybrid orbitals lie in a plane and are directed toward the corners of an equilateral triangle

– the unhybridized 2p orbital lies perpendicular to the plane of the three hybrid orbitals



Bonding in EthyleneBonding in Ethylene

H

H

H

H



sp sp Hybrid Orbitals Hybrid Orbitals

Two lobes of unequal size at an angle of 180°The unhybridized 2p orbitals are perpendicular to each other and to the line created by the axes of the two sp hybrid orbitals



Bond Orbital overlap Orbital Hybridisation

Predicted Bond Angles

Types of Bonds to Carbon

Example Name

C-C sp3-sp3 sp3 109.5o 4 sigma bonds

Ethane

C-H sp3-1s

C-C sp2-sp2, 2p-2p sp2 120o 3 sigma bonds and 1 pi bond

Ethylene

C-H sp2-1s

C-C sp-sp, two 2p-2p sp 180o 2 sigma bonds and 2 pi bonds

Acetylene

C-H sp-1s

H

H

H

H

H

H

H

H

H

H

H H



Organic Compounds

Hydrocarbons

Alcohols

Amines

Acids

Ketones

Aldehydes

Amides

Esters

Ethers

Nitrocompounds

Halocarbons

Nitriles



HYDROCARBONS contain only C and H atoms

ALIPHATIC hydrocarbons

AROMATIC Hydrocarbons must contain a

BENZENE ring

UNSATURATED hydrocarbons

contain at least 1 C–C multiple bond

SATURATED hydrocarbons

contain C–C and C–H single bonds only (ALKANES)

ALKENE contains the

C=C functional group

ALKYNE contains the

C≡C functional group



• Chemical formula CnH2n+2 n = 1, 2, 3, …

• CH4, methane, simplest one

• C2H6, ethane

• All have –ane ending– Follow a pattern

Prefix Number

Meth- One

Eth- Two

Prop- Three

But- Four

Pent- Five

Hex- Six

Hept- Seven

Oct- Eight

Non- Nine

Dec- Ten

Alkanes



Properties of Alkanes

Name Molecular formula

Melting point (oC)

Boiling point (oC)

Density at 20oC (g/mL)

Methane CH4 -183 -162 (Gas)

Ethane C2H6 -172 -89 (Gas)

Propane C3H8 -188 -42 (Gas)

Butane C4H10 -138 0 (Gas)

Pentane C5H12 -130 36 0.626

Hexane C6H14 -95 69 0.659

Heptane C7H16 -91 98 0.684

Octane C8H18 -57 126 0.703

Decane C10H22 -30 174 0.730

Dodecane C12H26 -10 216 0.749

Tetradecane C14H30 6 254 0.763

Hexadecane C16H34 18 280 0.775

Octadecane C18H38 28 316 (Solid)

Eicosane C20H42 37 343 (Solid)



Cycloalkanes

• Carbon atom chains in form of rings

• Name: cyclo + alkane name (i.e. Cyclobutane)

Cycloalkanes have higher bpt/mpt than straight chain alkanes with the same number of carbon atoms

Cyclopropane



Isomerism

• Isomers: compounds with same molecular formula but different structural formulas

• Differences in structure may give rise to differences in chemical and physical properties

• To name them choose the longest unbroken chain, and number the alkyl groups to obtain the lowest possible number (2, methylpropane)

Butane

Isobutane



They all have different Physical

Properties, Mpt, Bpt, densities

2, methylbutane Has the same

molecular formula as n-pentane, C5H12

2, 2 dimethylpropane

C4H10 – has two isomers, n-butane and isobutane (2-

methylpropane) CH3

CH3CH3

H

CH3

CH3CH3

CH3

CH3

CH3CH3

Isobutane

Isopentane

Neopentane



Reactions of Alkanes■ Combustion

■ Dehydrogenation

■ Halogenation

energyO2HCO2OCH 2224

alkene

RR High temp

Catalyst R R+ H H

Ethane Bromoethane

H

H

H

H

H

H + Br BrH e a t o r lig h t

H

H

H

H

H

Br + BrH



2-methylpentane (not 4-methylpentane)

The ending –ane means the C-C bonds are single. The Pent- tells us the longest chain is 5 carbons. They are numbered starting closest to the branch point.

3-methylhexane (not 2-ethylpentane or 4-methylhexane)

This is a saturated 6 carbon long chain with a methyl group attached to the third carbon.

2,2-dimethylbutane (not 2,2-methylbutane or 2-dimethylbutane)

Each addition to the carbon chain has its own number. The prefix di- inditcated there are two additional methyl groups.

3-bromo-1-chlorobutane (not 1-chloro-3-bromobutane or 2-bromo-4-chlorobutane)

The carbon chain is numbered from the end closest to the first additonal group. The additional groups are then named in alphabetical order irrespective of position number.

IUPAC rules

CH35

4

3

2

CH3

CH31

CH33

4

5

2CH31

CH36

CH31 2

3

CH34

CH3

CH3

1

2

3

CH34

Cl Br



2-Methylbutane

Alkane Alkyl group

Methane Methyl (CH3-)

Ethane Ethyl (CH3CH2-)

Propane Propyl (CH3CH2CH2-)

Butane Methyl (CH3CH2CH2CH2-)

CH34

3

2

CH3

CH31



Alkenes• Alkene: Unsaturated hydrocarbon that

contains one or more carbon-to-carbon double bonds– General formula of CnH2n

• All have –ene ending

• Simplest: ethylene, C2H4 3, methyl-1,4-pentadiene

1,3-Butadiene

1-Butene

CH3

CH2 CH2

CH2

CH2CH2

CH3



■ Addition reactions

Alkyl Halides

Alkyl hydrogen Sulphate

Alcohols

Dihaloalkanes

H

H

H

H

+ A X A

H H

HH

X

H

H

H

H

H

H H

HH

X

H

H H

HH

OSO3H

H

H H

HH

OH

X

H H

HH

X

H - X

H - O S O 3 H

H - O H

X - X

Reactions of Alkenes



■ Hydrogenation (another addition reaction)

■ Oxidation

■ Combustion

H

H

H

H

H H+P t or P d C a ta ly st

so lvent , p ressu reH

H H

HH

H

CH2 CH2 OHOH + MnO2

K M nO 4, - O H , H 2O

P t

etha no l, 1a tm

Cyclohexene CyclohexaneO2H2CO3OHC 22242

O2H2CO3OHC 22242



Polymers are large molecules containing many identical repeating units (100-1000000)

Polymerisation reaction is a repetition reaction which combines many small molecules of monomer (alkene) to form a polymer

Addition polymer is a polymer in which the monomer simply add together with no other products formed besides polymer

■ PolymerisationH

H

H

H

H

H

H

H

H

H

n

n

ethylene polyethylene

propylene polypropylene

vinyl chloridepoly(vinylchloride), PVC

teflon

Styrene polystyrene

tetrafluoroethene

H

H

CH3

H

H

CH3

H

H

H

Hn

H

H

Cl

H

H

Cl

H

H

H

H

n

n

F

F

F

F

H

F

F

F

F

H

n

n

H

H

H

H

H

H

H

H

n

n



Alkynes

• Alkyne: hydrocarbon that contains one or more carbon-to-carbon triple bonds

• General formula of CnH2n–2

• All have –yne ending

• Simplest: acetylene, C2H2

Acetylene

H

H



■ CombustionAlkynes are high energy compounds

Welding gas

■ Addition reactions

HH + 2.5 O2 2 CO2 + H2O

HH + H X

H

H

X

H

HH + X X

H

X

X

H

HH + H X

H X

XH

HH + H H

H

H

H

H

HH +

Excess

O3

then H 2O

O

OH

O

OH

Reactions of Alkynes



Acknowledgements

• JISC• HEA• Centre for Educational Research and Developmen

t• School of natural and applied sciences• School of Journalism• SirenFM• http://tango.freedesktop.org

http://www.jisc.ac.uk/

http://www.heacademy.ac.uk/

http://www.lincoln.ac.uk/cerd/

http://www.lincoln.ac.uk/cerd/

organic chemistry: structure of organic compounds

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