ByDr. Siham Lahsasni

Aliphatic Aromatic

straight Ring

Alkanes, Alkenes & Alkynes

Hydrocarbons : Carbon and Hydrocarbons : Carbon and Hydrogen atomsHydrogen atoms

Alkanes : CAlkanes : CnnHH2n+22n+2

NameMolecular Formula

MethaneCH4

EthaneC2H6

PropaneC3H8

ButaneC4H10

PentaneC5H12

HexaneC6H14

HeptaneC7H16

OctaneC8H18

NonaneC9H20

DecaneC10H22

Classes of carbon and Classes of carbon and HydrogenHydrogenPrimary carbon : CH3-CH2-CH3

Secondary carbon : CH3-CH2-CH3

Tertiary carbon : (CH3)2-CH-CH3

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

The length of the band: 1.54 AAngle: 109.5

Structural IsomerismStructural Isomerism

Different compounds with identical molecular formulas and different structures are called ISOMERS and the phenomenon is called ISOMERISM

Butane IsobutaneBoiling point 0 -12Melting point -138 -145

Pentane, C5H12 has three chain isomers.

Alkyl groupsAlkyl groupsAlkyl 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.

Butane

CH3-CH2-CH2-CH2- CH3-CHH2C

CH3

H3C C

CH3

CH3

n-Butyl Isobutyl tert.Butyl

Propane

CH3-CH2-CH2- CH3-CH

CH3

n-Propyl Isopropyl

IUPAC system of IUPAC system of nomenclaturenomenclature

1. Find and name the longest continuous carbon chain.

2. Identify and name groups attached to this chain.

3. Number the chain consecutively, starting at the end nearest a

substituent group.

4. Designate the location of each substituent group by an

appropriate number and name.

5. Assemble the name, listing groups in alphabetical order.

6. The prefixes di, tri, tetra etc., used to designate several groups

of the same kind, are not considered when alphabetizing.

7. Halogen substituent's are easily accommodated, using the

names: fluoro (F-), chloro (Cl-), bromo (Br-) and iodo (I-).

IUPAC NOMENCLATURE OF BRANCHED-IUPAC NOMENCLATURE OF BRANCHED-CHAIN ALKANESCHAIN ALKANES

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 .

H3CHC CH CH2

H2C CH2 CH3

CH3

CH3CH3CH2CH2CH2CHCH3

CH3

CH3CH2CH2CH2CHCH3

CH2

CH3

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

CH3CH2CH2CH2CHCH3

CH3

CH3CH2CH2CH2CHCH3

CH2

CH3

Substituent

Substituent

1

2

345 67 5

1

2346

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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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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. Cl is called chloro, Br called bromo, I called iodo, NO2 called nitro, CN called cyano

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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.

In case of deciding alphabetical order of many substituent disregard multiplying prefixes such as “di”and “tri”, “tetra”, “penta” ,

.…18

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

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CH3

CH3CCH2 CH2CH2CH3

CH2

CH3

3-Ethyl-3-methylhexane

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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Examples of the IUPAC Rules in Examples of the IUPAC Rules in PracticePractice

By inspection, the longest chain is seen to consist of six

carbons, so the root name of this compound will be hexane.

A single methyl substituent (colored red) is present, so this

compound is a methylhexane. The location of the methyl

group must be specified, since there are two possible

isomers of this kind. The IUPAC name is thus 3-

methylhexane. 22

Thus the parent chain will be the one with 4 substituents and the correct

IUPAc name of this compound is: 33--Ethyl-2,2,5-trimethylhexaneEthyl-2,2,5-trimethylhexane

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Examples of the IUPAC Rules in Examples of the IUPAC Rules in PracticePractice

By inspection, the longest chain is seen to consist of six

carbons, so the root name of this compound will be hexane.

A single methyl substituent (colored red) is present, so this

compound is a methylhexane. The location of the methyl

group must be specified, since there are two possible

isomers of this kind. The IUPAC name is thus 3-

methylhexane.

Drawing alkanesDrawing alkanes

n-Pentane

Physical PropertiesPhysical 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.

Preparation of alkanesPreparation of alkanes

1- Hydrogenation of unsaturated hydrocarbon:

2- Reduction of alkyl halides

a- Hydrolysis of Grignard reagent

CH2 CH2

Ni or Pd or Pt / H2

200, 300CH3 CH3

CH3CH2Br + Mg2+ Dry ether CH3CH2MgBr

Grignard reagent

CH3CH2MgBrH3O

+

CH3CH3 + Mg(OH)Br

b- Reduction by metal and acid

c- From coupling with metal

d- Using cuprate method

CH3CH2CH2Br + Zn2+ H

+

CH3CH2CH3

CH3CH2CH2CH2Br1)LiAlH4 / Ether

CH3CH2CH2CH3

+ ZnBr

2) H3O+

CH3 Br2 + 2 Na CH3 CH3 + 2 NaBr

(CH3CH2)2CuLi + CH3Br CH3CH2CH3

Reaction of alkanesReaction of alkanes1- Halogenation

RH + X2

Heat

or UV lightRX + HX

Alkyl HalideX2=Cl2 or Br2

Cl2 or Br2h

2 Cl

Cl + CH4 HCl + CH3

CH3 + Cl CH3Cl

if we have one type of carbone

If we have different type of carbone

H H

H

H

+ Cl Cl

Cl

Cl

Cl Cl + ClHHeat or UV light

excess

+ Cl Cl +Heat or UV light

CH3 CH3

Br

CH3

BrCH3 CH3

major

2- combustion of alkanes

160 kcal\mol for each methylene group

CH4 + 2 O2 CO2 + 2 H2O + 213 Kcal\mol

C2H6 + 7/2 O2 2 CO2 + 3 H2O + 373 Kcal\mol

Cycloalkanes :Cycloalkanes :             have one or more rings of carbon have one or more rings of carbon

atomsatoms

•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 CycloalkaneNaming CycloalkaneCount 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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Cis-Trans Isomerism in Cis-Trans Isomerism in CycloalkanesCycloalkanes

Rotation about C-C bonds in cycloalkanes is limited by the ring structure

There are two different 1,2-dimethylcyclopropane isomers, one with the two methyls on the same side (cis) of the ring and one with the methyls on opposite sides (trans)

Reaction of cycloalkanesReaction of cycloalkanesRing less stable

Ring more stable 5 and 6

HICH3CH2CH2I

H2SO4 / H2OCH3CH2CH2OH

H2/Ni

Heat or UVCH3CH2CH2CH3

Br2/CCl4AlBr3

BrCH2CH2CH2CH2Br

CH3

Br2/UV or Heat

CH3

Br

Cl2/heat or UVCl

Cyclohexane Ring Cyclohexane Ring StereochemistryStereochemistryPart I. How do you draw the cyclohexane ring

and position the substituents?Start by drawing the ring as one of the

following:

You may find it easier to keep your 3-D perspective if you darken the front pointing bonds using heavy bonds and wedges as follows:

Now you need to place the axial substituent bonds. These bonds will point upward towards the top of the page or downwards towards the bottom of the page (3 in each direction). The direction of the bonds alternate up-down-updown-up-down as you go from one carbon to the next:

Now that the axial bonds are in place, the equatorial become much easier if you keep one thought in mind - “bondangles around C with 4 bonds are optimally ~109.5 degrees”. Draw the equatorial bonds so that they form a 109.5 deg angle (i.e. >90 deg) with the axial bond drawn above. Make sure they point a little up or a little down rather than pointing directly towards the left or right margin. This will be extremely helpful latter when we determine the cis-trans relationship between substituents.

Part II. Determining the position of a substituent in the most stable conformer.

The axial positions above the ring point into the same space as is true for the axial positions below the ring (see figure) thereby putting the substituents very close together. However, the equatorial bonds point out away from the ring providing much more room for the substituents (compare below).

Therefore, if possible all substituents would prefer to be in

equatorial positions. However, if one is in the equatorial and one is axial, preference would be given to the larger group being equatorial.

Part III. Part III. Cis-trans relationship between cyclohexane Cis-trans relationship between cyclohexane substituentssubstituents

cis - refers to two substituents being on the same side of the ring (or double bond)

trans - refers to two substituents being on the opposite side of the ring (or double bond)

Relationship between Substituents Carbons

Axial - Axial Axial - Equatorial Equatorial - Equatorial

1 and 2 Trans Cis Trans

1 and 3 Cis Trans Cis

1 and 4 Trans Cis Trans

1 and 5 Cis Trans Cis

1 and 6 Trans Cis Trans