Chapter I Hydrocarbone Nomenclature and Reaction - PowerPoint Presentation

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Chapter I

Hydrocarbone

Nomenclature and Reaction

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Organic compounds are compounds that could be obtained from living organisms.

Inorganic compounds are compounds that came from nonliving sources.

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Chapter 1

3

Introduction

Organic ChemistryThe chemistry of the compounds of carbonThe human body is largely composed of organic compoundsOrganic chemistry plays a central role in medicine, bioengineering etc.VitalismIt was originally thought organic compounds could be made only by living things by intervention of

a “vital force”Fredrich Wöhler disproved vitalism in 1828 by making the organic compound urea from the inorganic salt ammonium cyanate by evaporation:

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There

are

more than 10 million compounds listed in Chemical Abstracts, and most of these are organic. Fortunately we can classify them into a few dozen families.

This classification is based on structural entities which have a chemical reactivity that is roughly predictable - so-called functional groups

.

functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules.

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Hydrocarbons

a 

hydrocarbon

 is an 

organic compound

 consisting entirely of hydrogen and carbon

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Alkanes

There are various subdivisions in the classification of hydrocarbons. One

family of hydrocarbons is called the alkanes, or sometimes paraffins

(from the Latin parum

affinis, meaning "little affinity" and thus implying a lack of reactivity) or aliphatics

(from the Greek word

aleiphar

meaning "fat or oil").

They are also called

saturated hydrocarbons.

All

alkanes

that are open chain (not rings) have the

general formula CnH2n+2

,

where

n is an integer.

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Alkanes

: C

nH2n+2

Molecular Formula

Name

CH

4

Methane

C

2

H

6

Ethane

C

3

H

8

Propane

C

4

H

10

Butane

C

5

H

12

Pentane

C

6

H

14

Hexane

C

7

H

16

Heptane

C

8

H

18

Octane

C

9

H

20

Nonane

C

10

H

22

Decane

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Classes of carbon and Hydrogen

Primary carbon :

CH

3-RSecondary carbon : R-CH

2-RTertiary carbon : (R)2-

CH-RQuaternary carbon: (R)4-

C

Hydrogens

are also referred to as 1º, 2º or 3º according to the type of carbon they are bonded to.

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Methane

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Alkyl groups

Alkyl groups are named by dropping the -

ane suffix of the

alkanes and adding the suffix -yl. Methane becomes a methyl group, ethane an ethyl group, etc.

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Alkyl groups

Alkanes

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ane

+

الأسم الأساسي (المقطع الاغريقي)

methane ane + meth

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IUPAC system of nomenclature

Find and name the longest continuous carbon chain.

Identify and name groups attached to this chain.

Number the chain consecutively, starting at the end nearest a substituent group.

Designate the location of each substituent group by an appropriate number and name.

Assemble the name, listing groups in alphabetical order.The prefixes di

, tri, tetra etc., used to designate several groups of the same kind, are not considered when alphabetizing.

Halogen substituent's

are easily accommodated, using the names:

fluoro

(F-),

chloro

(

Cl

-),

bromo

(Br-) and

iodo

(I-) also (-NH

2

) amino, (-NO

2

) nitro…

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1-

Locate the longest continuous chain of carbon atoms; this chain determines the parent name for the alkane. Sometimes, you may need to go around corners and zigzag to find the longest (parent) chain. (the parent chain is in blue):

If the parent chain for example has 6 carbon atoms, therefore, it is

a derivative of hexane and if it has 4 carbon atoms it is derivative of

butane and so on .

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2- Number the longest chain beginning with the end of the chain nearer to the substituent.

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3-

Use the numbers

obtained by application of rule 2

to designate the location of the substituent group.

The

parent name

is placed

last

; the

substituent group

, preceded by the

number

indicating its

location

on the chain, is placed

first

.

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4. When two or more substituents are present,

give each substituent a number

corresponding to its location on the longest chain.

The

substituent groups

are listed alphabetically regardless of their order of occurrence in the molecule.

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5

) When two or more substituents are identical, indicate this by the use of the prefixes

di-, tri-

, tetra-, and so on.

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6) When two substituents are present on the same carbon, use the number twice.

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7. When two chains of equal length compete for selection as the parent chain,

choose the chain with the greater number of substituents

.

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8. When branching occurs at an equal distance from both ends of the longest chain,

choose the name that gives the lower number at the first point of difference

.

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Drawing alkanes

n-Pentane

CH3-CH2-CH2-CH2-CH3

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Physical Properties

Methane, ethane, propane, and butane are gases; pentane through hexadecane are liquids; the homologues larger than hexadecane are solids.

The boiling points of alkanes increase with molecular weight. Branching reduces the boiling point, the more branching the lower the boiling point. Alkanes are almost completely insoluble in water.

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Reaction of

alkanes

1-Halogenatio

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2- combustion of

alkanes

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Cycloalkanes

:

     

Cycloalkanes

are alkanes that have carbon atoms that form a ring (called alicyclic compounds)Simple cycloalkanes are rings of (CH2)

n, or CnH2n

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Naming

Cycloalkane

Count the number of carbon atoms in the ring and the number in the largest substituent chain. If the number of carbon atoms in the ring is equal to or greater than the number in the substituent, the compound is named as an alkyl-substituted

cycloalkane For an alkyl- or halo-substituted

cycloalkane

, start at a point of attachment as C1 and number the

substituents

on the ring so that the second substituent has as low a number as possible.

Number the

substituents

and write the name

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Alkenes

Alkenes area class of 

HYDROCARBONS

 which contain only carbon and hydrogen. Two other terms which describe alkenes are unsaturated and olefins.UNSATURATED

 hydrocarbons contain either double or triple bonds. Since the compound is unsaturated with respect to hydrogen atoms, the extra electrons are shared between 2 carbon atoms forming double bonds in alkenes. Alkenes are also called OLEFINS

 because they form oily liquids on reaction with chlorine gas.All alkanes

that are open chain (not rings) have the

general formula CnH2n,

where

n is an integer

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HYBRIDISATION OF ORBITALS - ALKENES

+

3 SP

2

P

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Trigonal

Planar

π

σ

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Nomenclature of alkenes

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The

ene

suffix indicates an alkenes or cycloalkenes.The longest chain chosen for the root name must include both carbon atoms of the double bond.

The root chain must be numbered from the end nearest a double bond carbon atom. If the double bond is in the center of the chain, the nearest substituent rule is used to determine the end where numbering starts.

In

cycloalkenes

the double bond carbons are assigned ring locations C1 and C2. Which of the two is C1 may be determined by the nearest substituent rule.

Substituent groups containing double bonds are: 

    H

2

C=CH–  

Vinyl group

H

2

C=CH–CH

2

–  

Allyl

group

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3-Propyl-2-heptene

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3-Methyl

cyclohexene

2,3-DiMethyl

cyclohexene

3-Chloro-4-ethyl

cyclobutene

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Physical Properties of Alkenes

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Alkenes are non polar compounds.

Insoluble in water.

Soluble in non polar organic solvents.They are less dense than water.

Range of physical states: ≤ 4 C's are gases

5 - 17 C's are liquids

≥ 18 C's are solids

The alkenes has a boiling point which is a small number of degrees lower than the corresponding

alkanes

.

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n-Butane

1-Butene

1-Butene

1,2-DiChlorobutane

Reaction of

alkene

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2-Clorobutane

2-Butene

2-Hydroxybutane

2-Butene

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1-Chlorobutane

2-Chlorobutane

1-Butene

2-Hydroxybutane

1-Butene

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shape: Linear

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Identify the longest continuous chain of carbon atoms that contains the carbon-carbon triple bond. the -

ane

ending is changed to –

yne Number the carbon atoms of the longest continuous chain, starting at the end closest to the triple bond. .

The location and name of any substituent atom or group is indicated.

Nomenclature

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Reaction of

alkyne

1. Addition of halogen

3. Addition of hydrogen halide

2-

Addition of hydrogen

Alkenes and alkynes are generally more reactive than

alkanes

due to the electron density available in their pi

bonds

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Reaction of

alkyne

ketone

4- Addition of water : Hydration

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Acidity of

alkyne

More acidity

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• Benzene (C6H6) is the simplest aromatic hydrocarbon (or

arene).

• Benzene has four degrees of unsaturation, making it a highly unsaturated hydrocarbon. Benzene contains a planar 6-membered ring.•All C-

Cbond lengths are equal.•Kekuléproposed two equilibrated structures

• Whereas unsaturated hydrocarbons such as alkenes, alkynes and dienes readily undergo addition reactions, benzene does not.

Aromatic Compounds

Benzene

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Aside from the trivial names, we usually name

monosubstituted benzenes

with benzene as the parent. The name of the substituent is prefixed to theparent name.

monosubstituted benzenes

Nomenclature of Benzene Derivatives

For other monosubstituted benzenes, the presence of the substituent results in a new parent name (Common name).

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disubstituted

benzene

A disubstituted

benzene can be named with prefix numbers or by the ortho,meta, para system, which shows the positional relationships of the two groupsto each other on the ring.

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Aromatic substitution reactions

As described earlier benzene does not undergo addition reactions as do alkenes,

but substitution reactions of benzene are common. In these, a group or an atom

is substituted for a ring H – hence the reaction is referred to as an aromaticsubstitution reaction.

Halogenation:Treatment of benzene with bromine (Br2) in the presence of an iron(III) halide

catalyst yields bromobenzene, and Using chlorine gives chlorobenzene

Reactions of Benzene

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Nitration:

If benzene is treated with concentrated nitric acid, with concentrated sulfuric

acid as the catalyst, nitrobenzene is formed.

Sulfonation:

Treatment of benzene with fuming sulfuric acid gives benzenesulfonic acid.

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Alkylation:

When treated with a alkyl halides, denoted by R—X (see next topic) and

aLewis acid catalyst (AlX3 in this reaction), benzene is converted to an

alkylbenzene. This reaction is called a Friedel-Crafts alkylation after Charles Friedel, a French chemist, and James Crafts, an American chemist, who developed this reaction in 1877. The term alkylation means substitution by an

alkyl group.Acylation:

Friedel and Crafts developed a reaction similar to the alkylation reaction above. This type of reaction is called a Friedel-Crafts

acylation

because an

acyl

group (see later) , not an alkyl group, is substituted on the benzene ring. The symbol "

R" is used commonly in organic chemistry to denote an alkyl

substituent.