1.7_introduction to organic chemsitry (alkanes + alkenes)_notes to students

10/3/2011

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Organic Chemistry I

By:

Chemistry Department,

INTEC

Chapter Outline

• Introduction• Common Terminology in Organic ChemistryCommon Terminology in Organic Chemistry • Systematic Nomenclature• Isomerism• Alkanes• Alkenes• Halogenoalkanes• Alcohols• Alcohols• Bonding and reactivity• Quantitative organic chemistry• Applied organic chemistry

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Introduction

• Organic compounds consist of one or more b t d t i f ti lcarbon atoms and contain functional groups.

• The functional group determines the chemical properties of the compound.

• Examples of organic compounds: alkanes, alkenes alcohols carboxylic acidsalkenes, alcohols, carboxylic acids

Common Terminology in Organic Chemistry

• Homologous series: a series of compounds withHomologous series: a series of compounds with the same functional group and the same general formula, where one member differs from the next by CH2

• Empirical formula: represents the simplest whole b i f i l lnumber ratio of atoms in a molecule

• Molecular formula: represents the actual number of atoms in a molecule

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• Structural formula: represents the arrangement of

Cont’d

Structural formula: represents the arrangement of atoms in a molecule; usually written in expanded, condensed or skeletal form

Expanded formula Condensed formula Skeletal formula


• Homolytic fission: when a bond breaks with one

Cont’d

electron going to each atom (forming radicals)

• Heterolytic fission: when a bond breaks with the two electrons going to only one atom

• Free radical: a species that has a single unpaired electron

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Cont’d

• Nucleophile: a species which seeks out positive centres, and must have a lone pair of electrons to form a new covalent bond

• Electrophile: a species which seeks out negativeElectrophile: a species which seeks out negative centres, and accepts a lone pair of electrons to form a new covalent bond

Systematic Nomenclature:Alkanes

• From the structural formula of compound find theFrom the structural formula of compound, find the longest continuous carbon chain. Assign name for this chain using corresponding prefix and suffix –ane.

Number of carbon atoms

1 2 3 4 5 6 7 8

Prefix Meth- Eth- Prop- But- Pent- Hex- Hept- Oct-

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• Locate alkyl groups that are not part of the

Cont’d

Locate alkyl groups that are not part of the continuous chain and name them according to the number of carbon atoms present, with suffix –yl.

• The position of the branching alkyl group is numbered from the parent chain so that its position is at the lowest possible number.is at the lowest possible number.

• Numbers are separated from each other by commas and from words by hyphens.


• If an alkane compound contains two or more

Cont’d

If an alkane compound contains two or more identical branches, the following prefixes are used:

Number of branches

2 3 4

Prefix Di- Tri- Tetra-

• If an alkane compound has two or more different branching alkyl groups, they are placed in alphabetical order of the name.

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• If an alkane compound has other substituents such

Cont’d

If an alkane compound has other substituents such as halogen, it is added before the name of the alkane and numbered at the lowest position.

• If there are two or more of a similar substituents are attached to the alkane the prefix di‐ tri‐ or tetra‐ isattached to the alkane, the prefix di‐, tri‐ or tetra‐ is added accordingly.


• Example 1:

Cont’d

Example 1:

• Name: 22‐‐methylbutanemethylbutane

• Example 2:

4 3 2 1

7 6 5 4 3 2 1 • Example 2:

• Name: 44‐‐ethylethyl‐‐2,32,3‐‐dimethylheptanedimethylheptane

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• Example 3:

Cont’d

Example 3:

1122

33

44

5566

77

88

• Name: 2,62,6‐‐dimethyloctanedimethyloctane


• Example 4:

Cont’d

Example 4:

123

• Name: 11‐‐bromopropanebromopropane

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• Name the following organic compound using

Cont’d

Name the following organic compound using systematic names:

1. CH3‐CH2‐CH2‐CH2‐CH2‐CH3

2.

3.

Systematic Nomenclature:Alkenes

• The longest carbon chain for alkenes must contain at least one carbon with double bond(s)

Cont’d

contain at least one carbon with double bond(s).

• For alkenes, starting from 4 carbon atoms the compound have to be numbered according to the position of double bond(s) in the compound.

• The numbering should have the double bond(s) at the lowest possible number combination.

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• The prefix is similar with alkanes, but the ffi h t

Cont’d

suffix changes to –ene.

• If there are more than one double bond, the prefix di‐,tri‐ or tetra‐ is added accordingly.


Cont’d

• Example 1:1 2 3 4

• Name: 1,31,3‐‐butadiene/butabutadiene/buta‐‐1,31,3‐‐dienediene

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Cont’d

• Example 2:

1

2

3

4

5

6

• Name: 22‐‐methylmethyl‐‐22‐‐hexene/2hexene/2‐‐methylhexmethylhex‐‐22‐‐eneene


• Name the following compound using systematic

Cont’d

Name the following compound using systematic names.

1.

22.

3.

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Systematic Nomenclature:Alcohols

• For alcohols, the longest carbon chain should

Cont’d

o a co o s, e o ges ca bo c a s ou dconsist of at least one hydroxyl (‐OH) group(s).

• For alcohols, the suffix is –ol.

• Starting from 3 carbon atoms, the numbering is done so that the hydroxyl group is at the lowest possible position.possible position.

• If there are two or more of hydroxyl groups, prefix

di‐,tri‐ or tetra‐ is added accordingly.


Cont’d

•• Example 1:Example 1:

•• Name: Name: ethanolethanol

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Cont’d


123

•• Name: Name: 22‐‐propanol/propanpropanol/propan‐‐22‐‐olol


Cont’d


1234

•• Name: Name: 2,32,3‐‐butandiol/butanbutandiol/butan‐‐2,32,3‐‐dioldiol

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Cont’d

•• Name the following compounds using Name the following compounds using systematic names:systematic names:

1.1.

222.2.

3.3.

Systematic Nomenclature:Other Functional Groups

• For other functional groups, the rules for naming

Cont’d

For other functional groups, the rules for naming them are similar with alcohols.

• However, for aldehydes and carboxylic acids, the numbering starts with the carbonyl/carboxyl group. The carbonyl/carboxyl group are not usually given number, unless if there are more than one of the same functional groups Other functional group(s)same functional groups. Other functional group(s) attached to aldehydes or carboxylic acids are numbered, with the first carbon is the carbonyl/carboxyl groups.

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Cont’d

Substance Aldehyde Ketone Carboxylic Acid

Functional Group

Suffix -al -one -oic acid


Cont’d

Example 1:

Name: butanalbutanal

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Cont’d

Example 2:1

2

3

4

5

Name: 22‐‐methylpentanalmethylpentanal


Cont’d

Example 3:

2

13

4

5

Name: 22‐‐pentanone/pentanpentanone/pentan‐‐22‐‐oneone

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Cont’d

Example 4:

Name: ethanoic acidethanoic acid


Cont’d

Example 5:12

3

Name: 22‐‐chloropropanoic acidchloropropanoic acid

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Cont’d

• Name the following compounds using systematic names:

1.

2.


Cont’d

• Name the following compounds using systematic names:

3.

4.

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Isomerism

• Structural isomers: compounds that have i il l l f l b t diff tsimilar molecular formula but different structural formula.

• Structural isomers may have:– Different carbon chains (straight or branched)

– Different position of functional group in theDifferent position of functional group in the carbon chain

– Different functional groups

Isomerism

• Example of structural isomers (different carbon

Cont’d

Example of structural isomers (different carbon chains):

pentanepentane

2,22,2‐‐dimethylpropanedimethylpropane 22‐‐methylbutanemethylbutane

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Isomerism

Cont’d

• Example of structural isomers (different position of functional group):

11‐‐propanolpropanol 22‐‐propanolpropanol

Isomerism

• Example of structural isomers (different

Cont’d

a p e o st uctu a so e s (d e e tfunctional groups):

Ethyl methanoateEthyl methanoateP i idP i id

Molecular formula:C3H6O2

yyPropanoic acidPropanoic acid

Methyl ethanoateMethyl ethanoate

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Isomerism

• Geometric isomers: only occurs if there is a d bl b d i th l l d h b

Cont’d

double bond in the molecule, and each carbon has different atoms or groups attached to it.

• Geometrical isomers have restricted rotation about the double bond.

Isomerism

Cont’d

• Example of geometric isomers:

cis‐2‐butene trans‐2‐butene

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Isomerism • Optical isomers: exist in compounds where 4 different

groups are attached to a single carbon atom.

Cont’d

• The carbon is chiral (assymetrical).

• A pair of these isomers are called enantiomersenantiomers and their mirror image is not super‐imposable (or non‐superimposable mirror image)

• A mixture containing equal amount of optical isomers is A mixture containing equal amount of optical isomers iscalled a racemic mixtureracemic mixture.

Isomerism

Cont’d

Optical Isomers

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Alkanes

• General formula: CnH2n+2

• 1Combustion reaction:– General reaction:

CnH2n+2 + [(3n+1)/2]O2 nCO2+ (n+1)H2O

Example:‐ Example:

CH4 + 2O2 CO2 + 2H2O

Alkanes

Cont’d

• 2Substitution reaction in presence of UV light (X‐halogen, usually Cl2 or Br2):

– General reaction:

CnH2n+2 + X2 CnH2n+1‐X + HX

CnH2n+1X + X2 CnH2n‐X2 + HX

UV light

UV light

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Substitution Reaction of Alkanes

• in presence of UV light (X‐halogen, usually Cl2B ) E lor Br2):Example:

CH4 + Cl2 CH3‐Cl + HCl

CH3Cl + Cl2 CH2‐Cl2 + HCl

UV light

CH3Cl Cl2 CH2 Cl2 HClUV light

Alkanes

• Reaction mechanism: Homolytic free radicalHomolytic free radical

Cont’d

Reaction mechanism: Homolytic, free radical Homolytic, free radical substitutionsubstitution

1. Initiation step: Homolytic fission to free radicals

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Alkanes


Cont’d


2. Propagation step

Alkanes


Cont’d


2. Propagation step

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Alkanes

Cont’d

• Reaction mechanism: Homolytic, free radical Homolytic, free radical substitutionsubstitution

3. Termination step

Alkanes

Cont’d

• Reaction mechanism: Homolytic, free radical Homolytic, free radical substitutionsubstitution

3. Termination step

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Alkanes

Cont’d

• Reaction mechanism: Homolytic, free radical Homolytic, free radical additionaddition

3. Termination step

Alkenes

• General formula: CnH2n

• 3Addition reaction:– With hydrogen gas, at 150°C:

C H + H C HNi/Pt/Pd

CnH2n + H2 CnH2n+2

C3H6 + H2 C3H8

Ni/Pt/Pd

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Alkenes• 4Addition reaction:

– With halogens, at room temperature (X2=Cl2 orWith halogens, at room temperature (X2 Cl2 or Br2):

CnH2n + X2 CnH2nX2

CH3CH=CH2 + Br2 CH3CHBrCH2Br3 2 2 3 2

Addition reaction of alkene

‐ The change of colour for bromine, from red‐brown to colourless is a test for C=C group in ato colourless is a test for C=C group in a compound. For the test, bromine is dissolved in CCl4.

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Alkenes• 5Addition reaction

– With hydrogen halides (HI/HBr), at room temperature:

Cont’d

CnH2n + HX CnH2n+1‐X

CH3CH=CHCH3 + HBr CH3CH2CHBrCH3

Addition reaction of alkene

‐ With unsymmetrical alkenes, hydrogen atom goes to the carbon that has more hydrogen atomsto the carbon that has more hydrogen atoms bonded directly to it (Markovnikoff’s rule).

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Alkenes ‐Mechanism

•• Heterolytic, electrophilicHeterolytic, electrophilic addition reaction

Cont’d

1. Protonation to carbocation: electrophilic addition

2 N l hili tt k

2° cation‐more stable 1° cation

2. Nucleophilic attack

Alkenes

• Addition reaction \ b dditi i

Cont’d

Addition reaction..\abaddition.avi

Minor

Major

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Alkenes

• 6Oxidation reaction– Oxidizing agent: Potassium permanganate

Cont’d

Oxidizing agent: Potassium permanganate (KMnO4) in alkaline/acidic condition, at room temperature

CnH2n + [O] + H2O CnH2n(OH)2

CH3CH=CHCH3 + [O] + H2O CH3CH(OH)CH(OH)CH33 3

‐ Potassium permanganate will be reduced to manganese dioxide, which is seen as brown precipitate.

Alkenes

• 7Polymerisation reaction.Mechanism Animated\polymerization.avi

Cont’d

– Conditions: either high pressure and temperature (2000 atm, 250°C) or moderate pressure and temperature with catalyst addition (10 atm, 50°C, catalyst: titanium(IV) chloride + triethyl aluminium)

Additi ti– Addition reaction

n‐CnH2n ‐(CnH2n)‐n

1.7_introduction to organic chemsitry (alkanes + alkenes)_notes to students

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