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Organic Chemistry 有机化学


Organic Chemistry
DP Chemistry

What is Organic Chemistry?
? “Organic”

is a term that is used in a variety of ways:
?
? ?

“from living thi

ngs” “chemical free” “carbon-based”

Organic Chemistry is the study of carbon-based compounds

Carbon
?

Carbon is in Group IV of the periodic table Carbon has 4 valence electrons Carbon can form 4 covalent bonds Carbon can form single, double and triple bonds with a wide variety of elements forming nearly ten million known compounds

?

12
6

?

C

?

1s2 2s2 2p2

Tetravalent Carbon
Because carbon has four valence electrons, it forms four bonds with other elements to make up a full valence shell of 8. All valence electrons are involved in bonding. This bonding leads to tetrahedral shapes when all of the bonds involved are single bonds. Hydrocarbons are made up of carbon bonded to hydrogen, but many elements can and do take the place of hydrogen. Common elements that bond to carbon are N, O, S and the halogens (e.g. Cl, F). Carbon tetrachloride CCl4
Chlorine atoms Hydrogen atoms Carbon atom

Methane CH4

Carbon atom

Carbon Bonding

Structural Formula

Molecular Formula

H H

Single bond - ethane

H C C H H H

C2H6

H

H

Double bond - ethene

C C

H

H

C2H4

Carbon Bonding
Triple bond – ethyne (acetylene)

Structural Formula

Molecular Formula

H C C H

C2H 2

Cyclic– benzene

C6H 6

Fractional Distillation
Crude oil contains a mixture of hydrocarbons ranging from one carbon (C1) up to more than C24. Fractional distillation allows for these components or ?fractions? to be separated using a fractionating column. In this process, heat is applied to the bottom of the column and lighter compounds with lower boiling points rise to the top, while heavier compounds remain towards the bottom of the column.

Source: http://www.bbc.co.uk/schools/gcsebitesize/chemistry/usefulproductsoil/oil_and_oilproductsrev5.shtml

Hydrocarbons
Alkanes - hydrocarbons that
contain only single bonds (all ? bonds and no ? bonds - saturated). The table to the right shows the alkane homologous series (a family of compounds that have the same general formula differing by CH2). Formula – CnH2n+2 Straight-chain alkanes – carbons joined together to form a single chain with no branching. Structural formulae Number of C 1 2 3 4 5 6 7 8 Alkane Methane Ethane Propane Butane Pentane Hexane Heptane Octane

Methane

Ethane

Propane

Butane

Hydrocarbons
Alkenes – hydrocarbons that
contain one double bond between two carbon atoms.

Number of C 1 2 3 4 5 6 7 8

Alkene NA Ethene Propene Butene Pentene Hexene Heptene Octene

Formula – CnH2n

Isomers – compounds that have the same molecular formula, but different structure.
Alkenes have isomers because the double bond can be in a different location above C4. The location of the double bond is indicated by a numerical prefix counting from the shortest end. Condensed structural formulae
CH2 CH CH2 CH3 CH2 CH CH2 CH2 CH3

CH2

CH

CH

CH2

CH3

1-butene

1-pentene

2-pentene (NOT 3-pentene)

Hydrocarbons
Alkynes –
hydrocarbons that contain one triple bond between two carbon atoms.
Number of C 1 Alkyne NA

2 3

Ethyne Propyne
Butyne Pentyne Hexyne Heptyne Octyne

Formula – CnH2n-2 As with alkenes, a numerical prefix indicates the location of the triple bond.

4 5 6 7 8

Alkane b.p. trend
As alkanes get larger in size, the intermolecular forces increase due to a greater amount of dispersion forces. The table below and graph to the right show the trend in boiling point for simple, straight-chain alkanes. The longer the chain, the greater the forces between molecules

Types of Formulae
4 Types:
1. 2. Empirical –this shows the ratio of elements in the compound Molecular – shows the actual number of atoms in a compound, but no information about how they are arranged Structural – shows the arrangement of elements and all of the bonds between them. Most appropriate Condensed Structural – omits some or all of the bonds and may show identical groups bracketed together. These are not acceptable when asked for a structural formula. e.g. CH3(CH2)4CH3
Molecular Structural Formula Condensed Structural

3.

4.

Structural Isomers
Structural isomers are molecules that have the same molecular formula, but different structures. Butane Molecular formula: C4H10

Notice that changing the structure, changes some of the physical properties

Structural Isomers

Pentane Notice again that changing the structure, changes some of the physical properties. What pattern do you notice with these isomers? M.p./b.p. decreases with more branching

Naming Hydrocarbons
Examples of Simple Unbranched Alkanes
Name Molecular Formula CH4 Structural Formula CH4 Isomers Name Molecular Formula C6H14 Structural Formula CH3(CH2)4CH3 Isomers methane 1 hexane 5

ethane

C2H6

CH3CH3

1

heptane

C7H16

CH3(CH2)5CH3

9

propane

C3H8

CH3CH2CH3

1

octane

C8H18

CH3(CH2)6CH3

18

butane

C4H10

CH3CH2CH2CH3

2

nonane

C9H20

CH3(CH2)7CH3

35

pentane

C5H12

CH3(CH2)3CH3

3

decane

C10H22

CH3(CH2)8CH3

75

IUPAC IUPAC – The International Union of Pure and Applied Chemistry is a group of Chemists who devised a system of naming that allows for unique names to be applied to organic compounds. There are many compounds that also have common names, but this system allows us to speak a common language when naming these compounds. The simple alkanes above are the simplest examples.

IUPAC - Naming hydrocarbons
Problem Hexane C6H14 has 5 isomers. (See right)
How do we distinguish between them?
Note: these are shorthand notations where each line represents a bond between two carbon atoms

IUPAC “Quick” Rules for Alkane Nomenclature

1. Find and name the longest continuous carbon chain. 2. Identify and name groups attached to this chain. (These are called substituents.) 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 using the full name (e.g. ethyl before methyl). The prefixes di, tri, tetra etc., used to designate several groups of the same kind, are not considered when alphabetizing. Important notes: ? a hydrocarbon substituent becomes an alkyl group. (e.g. ethane becomes ethyl) ? Some substituents are “active sites” for reactions to occur (e.g. alcohols, ketones, alkenes) – these are then also referred to as functional groups.

IUPAC names for the isomers?

n-hexane

2-methyl pentane

3-methyl pentane

2,2 – dimethyl butane

2,3 – dimethyl butane

IUPAC “Quick” Rules for Alkane Nomenclature

1. Find and name the longest continuous carbon chain. 2. Identify and name groups attached to this chain. (These are called substituents.) 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 using the full name (e.g. ethyl before methyl). The prefixes di, tri, tetra etc., used to designate several groups of the same kind, are not considered when alphabetizing.

IUPAC – Naming Alkenes
IUPAC Rules for Alkene and Cycloalkene Nomenclature
1. The ene suffix (ending) indicates an alkene or cycloalkene. 2. The longest chain chosen for the root name must include both carbon atoms of the double bond. 3. 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. 4. The smaller of the two numbers designating the carbon atoms of the double bond is used as the double bond locator. If more than one double bond is present the compound is named as a diene, triene or equivalent prefix indicating the number of double bonds, and each double bond is assigned a locator number. 5. In cycloalkenes the double bond carbons are assigned ring locations #1 and #2. Which of the two is #1 may be determined by the nearest substituent rule. 6. Substituent groups containing double bonds are: H2C=CH– Vinyl group H2C=CH–CH2– Allyl group

But-1-ene

But-2-ene

Functional Groups
Functional groups are specific groups of atoms or bonds within a compound that are responsible for characteristic chemical properties of those substances.

Amines, Amides, Esters and Nitriles are HL only

Alcohols

Formula

Name

R-OH
Alcohols contain the hydroxyl group (OH) in place of a H atom in a hydrocarbon. Formula – CnH2n+1OH Compound suffix – “anol”

CH3OH
CH3(CH2)OH CH3(CH2)2OH CH3(CH2)3OH CH3(CH2)4OH CH3(CH2)5OH

Methanol
Ethanol Propanol Butanol Pentanol Hexanol

A number is used to indicate the location of the hydroxyl on a carbon chain in the same manner previously described.
Alcohols follow the same trend in b.p. as the hydrocarbons, but are all higher due to H-bonding.

Propan-1-ol

Aldehydes

Formula

Name

R-CHO
Aldehydes contain the carbonyl group (C=O) which is bonded to the last (terminal)carbon in a chain. Formula – CnH2nO Compound suffix – “anal”

HCHO
CH3CHO CH3CH2CHO CH3(CH2)2CHO CH3(CH2)3CHO CH3(CH2)4CHO

Methanal
Ethanal Propanal Butanal Pentanal Hexanal

No numbers are necessary for the naming of aldehydes as the group is on the terminal carbon.
Because of the carbonyl, there are permanent dipoles leading to stronger IM forces than alkanes, but weaker than alcohols.

Propanal

Ketones

R-COR?
Ketones contain the carbonyl group (C=O) which is bonded to a carbon that is not on the terminal end. This placement is how they differ from aldehydes.

Formula CH3COCH3 CH3(CH2)COCH3

Name Propanone Butanone

CH3(CH2)2COCH3 Pentanone

Formula – CnH2nO
Compound suffix – “anone” A number is used to indicate the location of the carbonyl on a carbon chain. Because of the carbonyl, there are permanent dipoles leading to stronger IM forces than alkanes, but weaker than alcohols.

CH3(CH2)3COCH3 Hexanone

Butan-2-one

Carboxylic Acids

Formula HCOOH CH3COOH CH3CH2COOH

Name

R-COOH
Carboxylic acids contain the carbonyl group (C=O) and the hydroxyl (OH) group. Formula – CnH2nO2 Compound suffix – “anoic acid” These compounds are polar towards the O atoms, away from the H atom, making the H atom available in acid/base rxns. Because of the carbonyl and the hydroxyl, Hydrogen bonding occurs between these molecules.

Methanoic acid
Ethanoic acid Propanoic acid

CH3(CH2)2COOH Butanoic acid CH3(CH2)3COOH Pentanoic acid CH3(CH2)4COOH Hexanoic acid

Ethanoic acid

Halides

Formula

Name

R-X
Halogenoalkanes contain the halide functional group, which is a halogen (X)atom in place of a hydrogen. Formula – CnH2n+1X Compound prefixes – “chloro”, “bromo”, “iodo” These compounds are named with the corresponding halogen atom at the beginning with the remainder of the compound named as per the rules for hydrocarbons. Again, a number is used to indicate the position of the halogen on the carbon chain. More than one halogen may be present

CH3Cl
CH3CH2Br CH3(CH2)2I CH3(CH2)3Cl CH3(CH2)4Br CH3(CH2)5I

chloromethane
Bromoethane Iodopropane Chloropropane Bromobutane Iodohexane

2-chloropropane

Primary, Secondary, Tertiary alcohols and halides
Primary (10): When a functional group is attached to a carbon that is bonded to only one other carbon atom. Secondary (20): When a functional group is attached to a carbon that is bonded to two other carbon atoms. Tertiary (30): When a functional group is attached to a carbon that is bonded to 3 other carbon atoms.

For you to do: Name the three alkyl halides above

Other functional groups
? R-NH2

? R-C6H5

? R-COR?

What functional groups can you see?
Benzene ring

Carboxylic acid IBUPROFEN

What functional groups can you see?
Carboxylic acid

Ester

What functional groups can you see?
Carboxylic acid Amine

An amino acid

Amines (AHL)
Formula Name Methylamine or Aminomethane Ethylamine or Aminoethane Propylamine or Aminopropane

R-NH2
Amines contain the amino group (NH2) somewhere in the hydrocarbon chain. Formula – RNH2 Compound suffix – “ylamine” OR Compound prefix – “amino” A number is used to indicate the location of the amino on a carbon chain in the same manner previously described.

CH3NH2 CH3(CH2)NH2 CH3(CH2)2NH2

1-butylamine

Amides (AHL)

R-CONH2
Amides contain the amino group (NH2) and a carbonyl group (C=O). Formula – RCONH2 Compound suffix – “anamide”

Formula
HCONH2

Name
Methanamide

CH3CONH2
CH3CH2CONH2

Ethanamide
Propanamide

Amides are the same structure as carboxylic acids with the amine group replacing the hydroxyl.

butanamide

Esters (AHL)

R-COOR?
Esters contain the carbonyl group (C=O) with an additional O attached to the carbon. Formula – RCOOR? Compound suffix – “yl oate” Esters are named in two parts from the carboxylic acid and alcohol that they are made from. The first part of the name comes from the alcohol and the second from the acid.

Nitriles (AHL)
Formula Name Methanenitrile Ethanenitrile

R-CN
Nitriles (aka cyanides) contain the cyano group which is a carbon triple bonded to a nitrogen. Formula – RCN Compound suffix – “nitrile” Nitriles are named by their hydrocarbon chain with nitrile added at the end.

CH3CN CH3(CH2) CN

CH3(CH2)2CN

Propanenitrile

pentanenitrile


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