13 - Hydrocarbons [Compatibility Mode]

Hydrocarbons & Functional Groups

“O h h h f b“Organic chemistry is the chemistry of carbon.

Th “ i ” fl h f h iThe name “organic” reflect the fact that organic

molecules are derived from living organisms Inmolecules are derived from living organisms. In

this unit will start by looking at four families ofthis unit will start by looking at four families of

organic molecules that are grouped together asorganic molecules that are grouped together as

the hydrocarbons. We will also look at some y

functional groups that define some of the other f g p f f

families of organic molecules.” 22

ORGANIC CHEMISTRY

• Organic chemistry is the chemistry of carbon.– There are three forms of pure carbon– There are three forms of pure carbon

• Diamond

• Graphite

33

ORGANIC CHEMISTRYORGANIC CHEMISTRY

Organic chemistry is the chemistry of carbon. There are three forms of pure carbon There are three forms of pure carbon

• Buckminsterfullerene“Bucky Balls”

44

HYDROCARBONS

– Organic molecules contain carbon combined with other elements.

– Organic molecules are grouped into families• Members of a family share common structural, physical, and y , p y ,

chemical characteristics.

– There are four families that contain molecules made f l b d h dof only carbon and hydrogen.

– Hydrocarbons• Alkanes• Alkenes• Alkynes• Aromatics 55

HYDROCARBONS

66

ALKANES

Alkanes are hydrocarbons that contain only carbon-carbon single bonds.carbon carbon single bonds. Every carbon atom participates in 4 single bonds,

either to another carbon or to a hydrogen.y g Every hydrogen atom is bonded to a carbon by a

single bond.

77

ALKANES

Alkanes are hydrocarbons that contain only carbon-carbon single bonds.carbon carbon single bonds.

88

ALKANES

Alkanes in which the carbons are connected in a straight chain are called normal alkanes.

C C C C C C

H

H

H H H H H

H nn--hexanehexanenn--hexanehexaneH HHHHH

Alkanes that are branched are called branched chain alkanes.

H

H

C

H H H

H

H

H

22--methylmethyl--pentanepentane22--methylmethyl--pentanepentane

99

C C C C C HH

H HHHH

yy ppyy pp

ALKANES

Alkanes, along with the other hydrocarbons, are non-polar.

They interact with each other only through London y y gdispersion forces.

This is why they have relatively low boiling and melting points.

1010

ALKANES

They interact with each other only through London dispersion forces.London dispersion forces. Note how the boiling points increase with molecular

weight.g

1111

MOLECULE IN THE NEWSMOLECULE IN THE NEWS

1212

MOLECULE IN THE NEWS MELAMINEMOLECULE IN THE NEWS:MELAMINE

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ORGANIC MOLECULES IN THE NEWS!! http://www.cbc.ca/health/story/2007/09/06/additives-lancet.html?ref=rssp y

http://www.medpagetoday.com/Psychiatry/ADHD-ADD/tb/6610

Quinoline yellowQuinoline yellow Sodium benzoateSodium benzoate

CarmoisineCarmoisine

1414

ALKANES Alkanes cannot be named based on their Alkanes, cannot be named based on their

molecular formulas For example all of the molecules shown below share For example, all of the molecules shown below share

the same molecular formula, C6H14(hexacarbon tetradecahydride?)( y )

C C C C C C

H

H

H

H H H H H

H

HHHHHH HHHHH

H

nn--hexanehexanenn--hexanehexane

H H H

C C C C C H

H

H

C

H H H

H H

C C C C C H

H

H

C

H H

H H

H

C C C C

H

H

C

H H

H H

H C C C C

H

H

C

H

H H

H

H

1515

H HHHH H HHHH H HH

CH

H

H

H HH

CH

H

H

22--methylmethyl--pentanepentane22--methylmethyl--pentanepentane 33--methylmethyl--pentanepentane33--methylmethyl--pentanepentane 2,22,2--dimethylbutanedimethylbutane2,22,2--dimethylbutanedimethylbutane 2,32,3--dimethylbutanedimethylbutane2,32,3--dimethylbutanedimethylbutane

ALKANES

Organic chemists use a systematic set of rules, called the IUPAC rules, to name organic molecules based on their structural formulas instead of their chemical formulas.

C C C C C C

H

H

H

H H H H H

H

HHHHHH HHHHH

H


H H H

C C C C C H

H

H

C

H H H

H H

C C C C C H

H

H

C

H H

H H

H

C C C C

H

H

C

H H

H H

H C C C C

H

H

C

H

H H

H

H

1616

H HHHH H HHHH H HH

CH

H

H

H HH

CH

H

H


CONSTITUTIONAL ISOMERS

When two or more molecules share the same molecular formula, but have different atomic molecular formula, but have different atomic connections, they are called constitutional isomers.

C C C C C C

H

H

H

H H H H H

H

HHHHHH HHHHH

H


H H H

C C C C C H

H

H

C

H H H

H H

C C C C C H

H

H

C

H H

H H

H

C C C C

H

H

C

H H

H H

H C C C C

H

H

C

H

H H

H

H

1717

H HHHH H HHHH H HH

CH

H

H

H HH

CH

H

H


CONFORMATIONS

Carbon-carbon single bonds are free to rotate

This leads to different shapes for some molecules

These should not be confused with isomers.

1818

CONFORMATIONS

All of the 3-dimensional models shown below are for the n-butane.for the n butane. They were generated by rotating the central carbon-

carbon bond. They all share the same structural formula.

1919C C C C

H

H

HHH

H

HH H H

CONFORMATIONS

All of the 3-dimensional models shown below are for the n-butane.for the n butane. They were generated by rotating the central carbon-

carbon bond.

2020

CONFORMATIONS

Switching from one conformation to another does not require the breaking and making of covalent bonds.

Switching from one isomer to another does require the breaking and making of covalent bondsthe breaking and making of covalent bonds.

nn--butanebutanenn--butanebutane 22--methylpropanemethylpropane22--methylpropanemethylpropane

2121C

H

H H

H HC C C C

H

H

HHH

HC C CH

H H

H

H

C C C C H

HH H H

H

CYCLOALKANES

When there are three or more carbons in a straight chain, the ends can be joined to make straight chain, the ends can be joined to make rings.

In naming these molecules, the prefix cyclo- is used to indicate the ring:

Skeletal structural formulas are used to represent the rings in structural formulas:

2222

CYCLOALKANES

In naming these molecules, the prefix cyclo- is used to indicate the ring.used to indicate the ring.

2323

CYCLOALKANESAs Parent ChainAs Parent ChainAs Parent ChainAs Parent Chain As Substituent GroupAs Substituent GroupAs Substituent GroupAs Substituent Group

C H

As Parent ChainAs Parent ChainAs Parent ChainAs Parent Chain As Substituent GroupAs Substituent GroupAs Substituent GroupAs Substituent Group

cyclopropaneC3H6

R cyclopropyl-

cyclobutane

C4H8

R cyclobutyl-

C5H10

cyclopentane R cyclopentyl-

2424cyclohexane

C6H12

Rcyclohexyl-y cyclohexyl

CYCLOALKANES

The carbon-carbon single bonds for the carbons in a ring are no longer free to rotate.a ring are no longer free to rotate. This leads to a new type of isomer Since the two structures share the same name they Since the two structures share the same name, they

are not constitutional isomers.

2525

CYCLOALKANES

CH3 CH3 CH3 CH3

HH HH

1,2-dimethylcyclohexane 1,2-dimethylcyclohexane

H

HH

H HH H

HH

H H

H HHH

H H

H HHCH3

H H

2626

CH3CH3 CH3H

CYCLOALKANESI hi h h th t i ti d Isomers which share the same atomic connections, and therefore, the same IUPAC name are called ste eoiso e sstereoisomers. When this occurs due to restricted rotation about a covalent

b d th ll d t i ibond, they are called geometric isomers The prefix cis- and trans- are used to distinguish geometric

isomersisomers.

2727

CYCLOALKANES

CH3 CH3 CH3 CH3

HH HH

cis-1,2-dimethylcyclohexane trans-1,2-dimethylcyclohexane

H

HHH H

H H

HCHH H

H HH

CHCH

HH H

H

CHH

CH3

2828

CH3CH3 CH3H

QUESTIONS

• Draw the condensed structural formulas for the following molecules:following molecules:

– 1-ethyl-2-methylcyclopentane

– 1,1-dimethylcyclobutane

– 1,1-dimethyl-2-propylcyclopropane

• Do any of these molecules have cis- and trans-Do any of these molecules have cis and transgeometric isomers?

2929

ALKENES ALKYNES & AROMATICALKENES, ALKYNES & AROMATICCOMPOUNDS

• The remaining three families of hydrocarbons are unsaturated.are unsaturated.

– Alkanes are saturated, which means they contain h i b f h d bthe maximum number of hydrogens per carbon.

• For alkanes CnH(2n+2)( )

– Alkenes, Alkynes and Aromatics are unsaturated which means they contain less than unsaturated, which means they contain less than the maximum number of hydrogens per carbon.

• Structurally, this means that they have carbon-carbon double or triple bonds

3030


Alkenes are hydrocarbons that contain at least 1 carbon-carbon double bond.carbon carbon double bond. Examples:

C CH H

C CH H

C CH CH2 CH2 CH2 CH3

C CH H

1-hexeneethene(ethylene)

3131


Alkynes are hydrocarbons that contain at least 1 carbon-carbon triple bond.carbon carbon triple bond. Examples:

C CH CH CH CH CHC CH H C CH CH2 CH2 CH2 CH3

1-hexyne

C CH H

ethyne yethyne(acetylene)

3232


Aromatics are unsaturated ring molecules They are often drawn to look like alkenes but they They are often drawn to look like alkenes, but they

behave much differently than alkenes. They have an alternating pattern of double and They have an alternating pattern of double and

single bonds within a ring. Benzene is an example

3333


3434


• The physical properties of all hydrocarbons are the samethe same

– The have essentially one noncovalent interaction, hi h i h L d di i fwhich is the London dispersion force.

– They have no electronegative atoms and therefore y ghave

no ion/ion interactions no ion/ion interactions

no dipole/dipole interactions

no hydrogenbonding interactions3535


• Naming of Alkenes and Alkynes work the same as for alkanes, with these added rules:as for alkanes, with these added rules:– The parent chain must include both carbons in all

double and triple bondsdouble and triple bonds.• Pick the longest chain that also contains all double and triple

bonds

The -ene ending is used of alkenes

The -yne ending is used for alkynes.

The number of the first carbon in the double or triple bond is The number of the first carbon in the double or triple bond is included in the name to locate the double or triple bond.

• Number the parent chain from the end that is closes to the fi d bl i l b d

3636first double or triple bond.


Naming of Aromatics is based on benzene: When the molecule is build on benzene the parent When the molecule is build on benzene, the parent

name is “benzene”. There are also many common names used to describe There are also many common names used to describe

aromatic compounds.

3737


Naming of Aromatics is based on benzene: Aromatic compounds can contain multiple aromatic Aromatic compounds can contain multiple aromatic

rings

3838


Benzo(a)pyrene found in tobacco smoke is converted to carcinogenic products in the liver converted to carcinogenic products in the liver which link to DNA and cause mutations.

3939


4040BenzoBenzo(a)(a)pyrenepyreneBenzoBenzo(a)(a)pyrenepyrene


Th ti l l f d i bi l There are many aromatic molecules found in biology Some aromatic compounds contain nitrogen and oxygen

atomsatoms For example, the nucleotide base Adenine, which is used to

make DNA and RNAmake DNA and RNA

NH2

N N

NH2

N

4141

N


Like cycloalkanes, some alkenes can have cis and trans isomerstrans isomers This is due to restricted rotation about the double-

bondbond.

Not all double bonds produce cis and trans isomers

4242


• Each carbon participating in the double bond must have two different bond must have two different substituents attached to them

A XC C

B Y

A ≠ B AND X ≠ YA ≠ B AND X ≠ Y

4343


Like cycloalkanes, some alkenes can have cis and trans isomerstrans isomers

4444

ALCOHOLS, CARBOXYLIC ACIDS & ESTERS

• In addition to the four families of hydrocarbons, there are also many other families of organic there are also many other families of organic molecules.

• These other families include elements other than carbon and hydrogen.y g

– They exhibit a wide range of chemical and physical properties.

The families are distinguished by a group of atoms – The families are distinguished by a group of atoms called a functional group

4545


Functional Group

“A functional group is an atom, group of atoms or bond that gives a molecule a particular set of chemical and physical p f p yproperties.”

4646


The carbon-carbon double bonds found in alkenes is an example of a functional group.is an example of a functional group.

A chemical property of a double is that it will absorb p p yhydrogen in the hydrogenation reaction.

4747


We look now at three families that are distinguished by a functional group that contains distinguished by a functional group that contains the element oxygen.

Al h l Alcohols Members of the alcohol family contain a hydroxyl

group.

4848


Alcohols The hydroxyl group comprises an oxygen with one The hydroxyl group comprises an oxygen with one

single bond to a hydrogen and another single bond to an alkane-type carbon

H H

C CH O H hydroxyl grouphydroxyl grouphydroxyl grouphydroxyl group

4949

H HAn An alkanealkane--type carbon atomtype carbon atomAn An alkanealkane--type carbon atomtype carbon atom

ethanolethanolethanolethanol



5050


Carboxylic acids Members of the carboxylic acid family contain a Members of the carboxylic acid family contain a

carboxylic acid group The carboxylic acid group comprises a hydroxyl The carboxylic acid group comprises a hydroxyl

group connected to a carbonyl group:

++++C

O

O H C

O

O H

5151

O Hcarbonyl groupcarbonyl groupcarbonyl groupcarbonyl group hydroxyl grouphydroxyl grouphydroxyl grouphydroxyl group carboxylic acid groupcarboxylic acid groupcarboxylic acid groupcarboxylic acid group


Carboxylic acids The present of the hydroxyl group next to the cabonyl The present of the hydroxyl group next to the cabonyl

group completely changes it properties.• The alcohol hydroxyl group and the carboxylic acid hydroxyl • The alcohol hydroxyl group and the carboxylic acid hydroxyl

group are chemically quite different, which is why molecules that have the carboxylic acid group are placed in a separate f il f th l h lfamily from the alcohols.

5252


Carboxylic acidsLater in the semester we will learn about some of these • Later in the semester we will learn about some of these chemical differences.

++++C

O

O H C

O

O H

5353

O Hcarbonyl groupcarbonyl groupcarbonyl groupcarbonyl group hydroxyl grouphydroxyl grouphydroxyl grouphydroxyl group carboxylic acid groupcarboxylic acid groupcarboxylic acid groupcarboxylic acid group


Carboxylic acids The carboxylic acid group can be attached to a The carboxylic acid group can be attached to a

hydrogen, an alkane-type carbon, or an aromatic-type carbon:

O OHH O

C OHH C OHCC

HH

H C OH

methanoicmethanoic acidacid(formic acid)(formic acid)


propanoicpropanoic acidacidpropanoicpropanoic acidacid benzoic acidbenzoic acidbenzoic acidbenzoic acid

HH

5454

( )( )( )( )



5555


Esters Chemically esters can be synthesized by reacting a Chemically, esters can be synthesized by reacting a

carboxylic acid with and alcohol:

C

O

O H H O C+ C

O

O C H O+ H

carboxylic carboxylic acidacid

carboxylic carboxylic acidacid

alcoholalcoholalcoholalcohol esteresteresterester waterwaterwaterwater

5656


Esters Chemically esters can be synthesize by reacting a Chemically, esters can be synthesize by reacting a

carboxylic acid with and alcohol:

C

O

O CH2CH2CH3 CH3

Carboxylicacid part

Alcoholpart

5757

acid part p

Ethyl Ethyl propanoatepropanoateEthyl Ethyl propanoatepropanoate


Carboxylic acids The carboxylic acid group can be attached to a The carboxylic acid group can be attached to a

hydrogen, an alkane-type carbon, or an aromatic-type carbon:

O OHH O

C OHH C OHCC

HH

H C OH



propanoicpropanoic acidacidpropanoicpropanoic acidacid benzoic acidbenzoic acidbenzoic acidbenzoic acid

HH

5858

( )( )( )( )


• As we saw with the hydrocarbons, the physical properties of organic molecules depend on the p p g pnoncovalent intermolecular interactions which attract one one molecule to another.– With hydrocarbons, there is only one type of

noncovalent interaction:• Induced dipole/Induced dipole (London dispersion force)

The presence of the electronegative oxygen makes – The presence of the electronegative oxygen makes alcohols, carboxylic acids and esters polar molecules, these families, therefore, have at least two types of

l i inoncovalent interactions:• Induced dipole/Induced dipole (London dispersion force)• Dipole/Dipole 5959• Dipole/Dipole


• As we saw with the hydrocarbons, the physical properties of organic molecules depend on the properties of organic molecules depend on the noncovalent intermolecular interactions which attract one one molecule to another.– Alcohols and Carboxylic acids also have a hydroxyl

group with a hydrogen bonded to an oxygen This group with a hydrogen bonded to an oxygen. This allows them to form hydrogen bonds with each other. Therefore, carboxylic acids have at least three , ydifferent noncovalent interactions:

• Induced dipole/Induced dipole (London dispersion force)• Dipole/Dipole• Hydrogen bond

6060


• To summarize, the types of noncovalent interact ions that each family can participate in include:ions that each family can participate in include:– Hydrocarbons (Alkanes, Alkenes, Alkynes &

A o atics)Aromatics)• Induced dipole/Induced dipole (London dispersion force)

– Esters• Induced dipole/Induced dipole (London dispersion force)

Di l /Di l• Dipole/Dipole

– Alcohols & Carboxylic acids• Induced dipole/Induced dipole (London dispersion force)• Dipole/Dipole

6161

• Hydrogen bond


These interactions are illustrated in Figure 4.23 of your textbook.of your textbook.

alcoholsalcoholsalcoholsalcoholsalcoholsalcoholsalcoholsalcohols

6262

estersestersestersesters

carboxylic acidscarboxylic acidscarboxylic acidscarboxylic acids


• Boiling points are a good measure of the strength of the noncovalent interactions between molecules.– The stronger the interactions the higher the boiling – The stronger the interactions, the higher the boiling

point will be.

– Since all molecules have the London dispersion interaction, the boiling points of molecules is expected to increase with temperatureexpected to increase with temperature.

– The next slide shows a chart using the data found in Table 4.7 of Raymond, in which the boiling points for alcohols, carboxylic acids and esters are plotted against molecular weight 6363against molecular weight.

ALCOHOLS, CARBOXYLIC ACIDS & ESTERS– As expected the boiling – As expected, the boiling

points for members of all three families increases with molecular weight due t th L d di i to the London dispersion interactions.

– For a given molecular i ht th l h l d {{°°

C}C}{{°°C}C}

weight, the alcohols and carboxylic acids have a higher boiling point than esters, this is because they Po

int

{Point

{Point

{Point

{

can form hydrogen bonds and esters cannot.

– The carboxylic acids have Boiling

Boiling

Boiling

Boiling

a slightly higher boiling point than alcohols, because they can form two hydrogen bonds with a

BBBB

hydrogen bonds with a neighboring molecule (See Figure 4.23 in Raymond)

6464Molecular Weight {g/mol}Molecular Weight {g/mol}Molecular Weight {g/mol}Molecular Weight {g/mol}


• Another distinguishing characteristic of many of the families is odor.

– You nose is actually a highly sensitive chemical detector.

– The members of different families can interact differently with the receptors in your nose to produce smells that are characteristic of the families they belong tto.

– For example:• Carboxylic acids produce the pungent, sometime unpleasant odors

associated with ripe cheeses, rancid butter and vomit.

Esters on the other hand produce the sweet often pleasant order • Esters, on the other hand, produce the sweet, often pleasant order associated with flowers, perfumes and various natural and artificial flavorings. The next slide shows Figure 4.24 from Raymond, which gives some specific examples. 6565


Examples of some of some flavorable esters:

6666

THE END

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13 - Hydrocarbons [Compatibility Mode]

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