Lecture 9 - Alcohols and Alkyl Halides

General

Organic ChemistryTwo credits

Second Semester 2009

King Saud bin Abdulaziz University for Health Science

Reference Book: Organic Chemistry: A Brief Course, by Robert C. Atkins and Francis A. CareyThird Edition

Instructor: Rabih O. Al-Kaysi, PhD.

Chapter 3Chapter 3

Alcohols and Alkyl Halides

Lecture 9

Functional GroupsFunctional Groups

a structural unit in a molecule responsible for itsa structural unit in a molecule responsible for itscharacteristic behavior under a particular set ofcharacteristic behavior under a particular set ofreaction conditionsreaction conditions

Functional GroupFunctional Group

AlcoholAlcohol ROHROH

Alkyl halideAlkyl halide RRXX ( (XX = F, Cl, Br, I) = F, Cl, Br, I)

Families of organic compoundsFamilies of organic compoundsand their functional groupsand their functional groups

IUPAC NomenclatureIUPAC Nomenclature

of Alkyl Halidesof Alkyl Halides

The two that are most widely used are:The two that are most widely used are:functional class nomenclaturefunctional class nomenclaturesubstitutive nomenclaturesubstitutive nomenclature

Both types can be applied to alcohols andBoth types can be applied to alcohols andalkyl halides.alkyl halides.


There are several kinds of IUPAC nomenclature.There are several kinds of IUPAC nomenclature.

Name the alkyl group and the halogen asName the alkyl group and the halogen asseparate words (separate words (alkylalkyl + + halidehalide))

Functional Class Nomenclature of Alkyl HalidesFunctional Class Nomenclature of Alkyl Halides

CHCH33FF CHCH33CHCH22CHCH22CHCH22CHCH22ClCl

CHCH33CHCH22CHCHCHCH22CHCH22CHCH33

BrBr

HH

II

Name the alkyl group and the halogen asName the alkyl group and the halogen asseparate words (separate words (alkylalkyl + + halidehalide))

Functional Class Nomenclature of Alkyl HalidesFunctional Class Nomenclature of Alkyl Halides

CHCH33FF CHCH33CHCH22CHCH22CHCH22CHCH22ClCl

CHCH33CHCH22CHCHCHCH22CHCH22CHCH33

BrBr

Methyl fluorideMethyl fluoride Pentyl chloridePentyl chloride

1-Ethylbutyl bromide1-Ethylbutyl bromide Cyclohexyl iodideCyclohexyl iodide

HH

II

Name as halo-substituted alkanes.Name as halo-substituted alkanes.

Number the longest chain containing theNumber the longest chain containing thehalogen in the direction that gives the lowesthalogen in the direction that gives the lowestnumber to the substituted carbon.number to the substituted carbon.

Substitutive Nomenclature of Alkyl HalidesSubstitutive Nomenclature of Alkyl Halides

CHCH33CHCH22CHCH22CHCH22CHCH22FF CHCH33CHCHCHCH22CHCH22CHCH33

BrBr

CHCH33CHCH22CHCHCHCH22CHCH33

II

Name as halo-substituted alkanes.Name as halo-substituted alkanes.

Number the longest chain containing theNumber the longest chain containing thehalogen in the direction that gives the lowesthalogen in the direction that gives the lowestnumber to the substituted carbon.number to the substituted carbon.


CHCH33CHCH22CHCH22CHCH22CHCH22FF CHCH33CHCHCHCH22CHCH22CHCH33

BrBr1-Fluoropentane1-Fluoropentane

3-Iodopentane3-Iodopentane

2-Bromopentane2-BromopentaneCHCH33CHCH22CHCHCHCH22CHCH33

II


Halogen and alkyl groupsHalogen and alkyl groupsare of equal rank when are of equal rank when it comes to numberingit comes to numberingthe chain.the chain.

Number the chain in theNumber the chain in thedirection that gives the direction that gives the lowest number to thelowest number to thegroup (halogen or alkyl)group (halogen or alkyl)that appears first.that appears first.

CHCH33

ClCl ClCl

CHCH33


5-Chloro-2-methylheptane5-Chloro-2-methylheptane

2-Chloro-5-methylheptane2-Chloro-5-methylheptane

CHCH33

ClCl ClCl

CHCH33


of Alcoholsof Alcohols

Name the alkyl group and add "alcohol" as aName the alkyl group and add "alcohol" as aseparate word.separate word.

Functional Class Nomenclature of AlcoholsFunctional Class Nomenclature of Alcohols

CHCH33CHCH22OHOH

CHCH33CHCHCHCH22CHCH22CHCH22CHCH33

OHOH

CHCH33CCHCCH22CHCH22CHCH33

OHOH

CHCH33

Name the alkyl group and add "alcohol" as aName the alkyl group and add "alcohol" as aseparate word.separate word.

Functional Class Nomenclature of AlcoholsFunctional Class Nomenclature of Alcohols

CHCH33CHCH22OHOH


OHOH


OHOH

CHCH33

Ethyl alcoholEthyl alcohol

1-Methylpentyl alcohol1-Methylpentyl alcohol

1,1-Dimethylbutyl1,1-Dimethylbutylalcoholalcohol

Name as "alkanols." Replace -e ending of alkaneName as "alkanols." Replace -e ending of alkanename by -ol.name by -ol.

Number chain in direction that gives lowest numberNumber chain in direction that gives lowest numberto the carbon that bears the —OH group.to the carbon that bears the —OH group.

Substitutive Nomenclature of AlcoholsSubstitutive Nomenclature of Alcohols

CHCH33CHCH22OHOH


OHOH


OHOH

CHCH33

Name as "alkanols." Replace -e ending of alkaneName as "alkanols." Replace -e ending of alkanename by -ol.name by -ol.

Number chain in direction that gives lowest numberNumber chain in direction that gives lowest numberto the carbon that bears the —OH group.to the carbon that bears the —OH group.


CHCH33CHCH22OHOH


OHOH


OHOH

CHCH33

EthanolEthanol

2-Hexanol2-Hexanol2-Methyl-2-pentanol2-Methyl-2-pentanol

OHOH

CHCH33


Hydroxyl groups outrank Hydroxyl groups outrank alkyl groups when alkyl groups when it comes to numberingit comes to numberingthe chain.the chain.

Number the chain in theNumber the chain in thedirection that gives the direction that gives the lowest number to thelowest number to thecarbon that bears thecarbon that bears theOH groupOH group

CHCH33

OHOH


6-Methyl-3-heptanol6-Methyl-3-heptanol

5-Methyl-2-heptanol5-Methyl-2-heptanol

OHOH

CHCH33

CHCH33

OHOH

Classes of AlcoholsClasses of Alcohols

and Alkyl Halidesand Alkyl Halides

Alcohols and alkyl halides are classified asAlcohols and alkyl halides are classified asprimaryprimarysecondarysecondarytertiarytertiary

according to their "degree of substitution."according to their "degree of substitution."

Degree of substitution is determined by countingDegree of substitution is determined by countingthe number of carbon atoms directly attached tothe number of carbon atoms directly attached tothe carbon that bears the halogen or hydroxyl group.the carbon that bears the halogen or hydroxyl group.

ClassificationClassification

CHCH33CHCH22CHCH22CHCH22CHCH22FF

CHCH33CHCHCHCH22CHCH22CHCH33

BrBr

primary alkyl halideprimary alkyl halide

secondary alkyl halidesecondary alkyl halide

ClassificatioClassificationn


OHOH

CHCH33

tertiary alcoholtertiary alcohol

HH

OHOH

secondary alcoholsecondary alcohol

Bonding in AlcoholsBonding in Alcohols

and Alkyl Halidesand Alkyl Halides

HH

HH

HH

alcohols and alkyl halides are polaralcohols and alkyl halides are polar

= 1.7 D= 1.7 D = 1.9 D= 1.9 D

HH

HH

CC OO

HH

HH

CC ClCl++

––––++

++

Dipole MomentsDipole Moments

+ + – –

– – + +

+ + – – + + – – + + – –

Dipole-Dipole Attractive ForcesDipole-Dipole Attractive Forces

+ + – –

– – + +

+ + – – + + – – + + – –

Dipole-Dipole Attractive ForcesDipole-Dipole Attractive Forces

Boiling pointBoiling point

Solubility in waterSolubility in water

DensityDensity

Physical Properties of Physical Properties of

Alcohols and Alkyl Halides:Alcohols and Alkyl Halides:

Intermolecular ForcesIntermolecular Forces

4444 4848 4646

-42-42 -32-32 +78+78

00 1.91.9 1.71.7

CHCH33CHCH22CHCH33 CHCH33CHCH22FF CHCH33CHCH22OHOH

MolecularMolecularweightweight

BoilingBoilingpoint, °Cpoint, °C

DipoleDipolemoment, Dmoment, D

Effect of Structure on Boiling PointEffect of Structure on Boiling Point

Just for general knowledge, will not be tested on

4444

--4242

00

CHCH33CHCH22CHCH33




Intermolecular forcesIntermolecular forcesare weak.are weak.

Only intermolecularOnly intermolecularforces are inducedforces are induceddipole-induced dipoledipole-induced dipoleattractions.attractions.



4848

-32-32

1.91.9

CHCH33CHCH22FF




A polar molecule;A polar molecule;therefore dipole-dipoletherefore dipole-dipoleand dipole-inducedand dipole-induceddipole forces contributedipole forces contributeto intermolecular to intermolecular attractions.attractions.



4646

+78+78

1.71.7

CHCH33CHCH22OHOH




Highest boiling point;Highest boiling point;strongest intermolecularstrongest intermolecularattractive forces.attractive forces.

Hydrogen bonding isHydrogen bonding isstronger than otherstronger than otherdipole-dipole attractions.dipole-dipole attractions.



++––

––++

Hydrogen bonding in ethanolHydrogen bonding in ethanol


Boiling point increases with increasingBoiling point increases with increasingnumber of halogensnumber of halogens

CHCH33ClCl -24°C-24°C

CHCH22ClCl22 40°C40°C

CHCHClCl33 61°C61°C

CCClCl44 77°C77°C

CompoundCompound Boiling PointBoiling Point

Even though CClEven though CCl4 4 is the only compound in this list without a is the only compound in this list without a

dipole moment, it has the highest boiling point.dipole moment, it has the highest boiling point.

Induced dipole-induced dipole forces are greatest in Induced dipole-induced dipole forces are greatest in CClCCl44 because it has the greatest number of Cl atoms. because it has the greatest number of Cl atoms.

Cl is more polarizable than H. Cl is more polarizable than H.

But trend is not followed when halogenBut trend is not followed when halogenis fluorineis fluorine

CHCH33CHCH22FF -32°C-32°C

CHCH33CHCHFF22 -25°C-25°C

CHCH33CCFF33 -47°C-47°C

CCFF33CCFF33 -78°C-78°C



But trend is not followed when halogenBut trend is not followed when halogenis fluorineis fluorine

CHCH33CHCH22FF -32°C-32°C

CHCH33CHCHFF22 -25°C-25°C

CHCH33CCFF33 -47°C-47°C

CCFF33CCFF33 -78°C-78°C


Fluorine is not very polarizable and induced dipole-Fluorine is not very polarizable and induced dipole-induced dipole forces decrease with increasing induced dipole forces decrease with increasing fluorine substitution.fluorine substitution.


Solubility in waterSolubility in water

Alkyl halides are insoluble in water.Alkyl halides are insoluble in water.

Methanol, ethanol, isopropyl alcohol areMethanol, ethanol, isopropyl alcohol arecompletely miscible with water.completely miscible with water.

The solubility of an alcohol in waterThe solubility of an alcohol in waterdecreases with increasing number of decreases with increasing number of carbons (compound becomescarbons (compound becomesmore hydrocarbon-like).more hydrocarbon-like).

++––

––

++

––++

Hydrogen Bonding Between Ethanol Hydrogen Bonding Between Ethanol and Waterand Water


DensityDensity

Alkyl fluorides and alkyl chlorides Alkyl fluorides and alkyl chlorides areareless dense than water.less dense than water.

Alkyl bromides and alkyl iodides are Alkyl bromides and alkyl iodides are more dense than water.more dense than water.

All liquid alcohols have densities of All liquid alcohols have densities of about 0.8 g/mL.about 0.8 g/mL.

Preparation of Alkyl Halides fromPreparation of Alkyl Halides from

Alcohols and Hydrogen HalidesAlcohols and Hydrogen Halides

ROH + HX ROH + HX RX + H RX + H22OO

RROOHH + + HHXX R RXX + + HHOOHH

Hydrogen halide reactivityHydrogen halide reactivity

HHFF HHClCl HHBrBr HHII

Reaction of Alcohols with Hydrogen HalidesReaction of Alcohols with Hydrogen Halides

least reactiveleast reactive most reactivemost reactive

Alcohol reactivityAlcohol reactivity

CHCH33OOHH RCH RCH22OOH H RR22CHCHOOH H RR33CCOOHH

MethanolMethanol PrimaryPrimary SecondarySecondary TertiaryTertiary

RROOH H + + HHXX R RXX + + HHOOHH

Reaction of Alcohols with Hydrogen HalidesReaction of Alcohols with Hydrogen Halides

least reactiveleast reactive most reactivemost reactive

(CH(CH33))33CCOHOH + H + HClCl (CH(CH33))33CCClCl + H + H22OO

78-88%78-88%

25°C25°C

Preparation of Alkyl HalidesPreparation of Alkyl Halides

73%73%

80-100°C80-100°C

OHOH ++ HHBrBr

BrBr ++ HH22OO

Documents

Lecture 9 - Alcohols and Alkyl Halides