Organic Chemistry

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Organic Chemistry

The Chemistry of Carbon

Intramolecular Forces• Forces of electrostatic attraction within a

molecule.• Occur between the nuclei of the atoms and their

electrons making up the molecule (i.e. covalent bonds)

• Must be broken by chemical means and form new substances when broken.

• Determine the chemical properties of a substance.

Intermolecular Forces• Forces of attraction between two molecules (i.e.

London dispersion forces, dipole–dipole interactions or hydrogen bonds)

• Much weaker than Intramolecular forces and are much easier to break.

• Physical changes (changes of state) break or weaken these forces.

• Do not form new substances when broken.• These forces determine the physical properties

of a substance.

London Dispersion Forces• These forces are based on the simultaneous

attraction of the electrons of one molecule by the positive nuclei of neighbouring molecules

• The strength of the force is directly related to the number of electrons and protons in a given molecule

• The greater the number of electrons and protons the greater the force

Dipole-Dipole Forces• Occur between polar molecules having dipoles.• Molecules with dipoles are characterized by

oppositely charged ends that are due to an unequal distribution of charge on the molecule.

• The polarity of a molecule is determined by both the polarity of the bond and the shape of the molecule.

• These forces are based on the simultaneous attraction of the electrons of one dipole by the dipoles of neighbouring molecules.

• The strength of the force is related to the polarity of the given molecule.

Hydrogen Bonds• These forces are a type of dipole – dipole

interaction.• Occur between Hydrogen atoms in one molecule

and highly electronegative atoms (F, O, N) in another.

• The strongest of the Intermolecular forces and are about 1/10 the strength of a covalent bond.

Characteristics of Organic Compounds1. Made of carbon atoms in chains or rings.

2. Contain covalent bonds.

3. Principle intermolecular force is London Dispersion.

4. One molecular formula can represent many different compounds (isomers).

5. Properties are determined by the presence of certain groups within the compound (functional groups).

Why are there so many Organic Compounds?

1. Carbon has 4 valence electrons therefore 4 bonds.

2. Carbon readily bonds with other carbon atoms forming chains, branched or cyclic compounds.

3. Carbon also readily bonds with other elements such as O, N, S, halogens.

General Naming Rules for Organics

• The prefix indicates the number of carbon atoms in the chain.

# of C’s prefix

1 meth

3 prop

5 pent

7 hept

10 dec

• The ending indicates the functional groups in the structure.

C=C “ene”

-OH “ol

Alkanes

• All C-C single bonds

• General Formula CnH2n+2, where “n” is the number of carbon atoms in the chain.

Naming

1. Use the correct prefix to indicate the number of carbons.

2. Ending is “ane”

Drawing Organic Compounds

There are 3 ways to draw an organic compound.

1. Structural Diagram: shows all bonds in the molecule. (the H’s are generally left off to keep structures clean)

2. Condensed Structure: no bonds but all atoms are shown in sequence. (Must put bonds between C’s in for cyclo’s)

3. Line (Skeletal) Diagram: carbon atoms are implied by the vertices (including ends) in the structure, H’s are not shown but any other atoms are written.

Structural Condensed Line

butane CH3CH2CH2CH3

orCH3(CH2)2CH3

1-propanol CH3CH2CH2OHor

HOCH2CH2CH3

methoxyethane CH3OCH2CH3

Naming Branched Hydrocarbons1. Identify the longest continuous chain or ring of

carbon atoms.2. Number the carbons from the end that gives the

lowest sum for the numbers of the branches.3. Name each branch and indicate its location with a

number.4. List the branches in alpha order before the prefix

for the number of carbons.5. Commas separate numbers and hyphens

separate numbers from words.

6. If there is more than 1 of the same branch Greek prefixes are used to indicate this but the prefix is not counted in determining alpha order.

Common Branches

-Br bromo isopropyl

-Cl chloro

-F fluoro tert-butyl

-I iodo

-CH3 methyl

-CH2CH3 ethyl -NH2 amino

-OH hydroxy -NO2 nitro

Alkenes• Contain 1 or more C=C double bond.• When naming use the suffix “ene”.• The position of the double bond is indicated for

alkenes with 4 or more carbons.

Alkynes• Contain at least 1 C≡C bond.• When naming use the suffix “yne”.• The position of the triple bond is indicated for

alkynes with 4 or more carbons.

Types of Isomers• Isomers are molecules with the same formula

but different structures.• There are different types of isomers

1. Structural: are in the same organic family (i.e. 2 alkenes) but have a different arrangement of the atoms.

2. Functional: same formula but are in different organic families (i.e. an alcohol and ether)

3. Geometric: differ in the placement of groups around a double bond. (“cis-trans” isomers)

4. Optical: mirror images of each other that cannot be superimposed onto each other.

Geometric Isomers (“cis-trans”)• Double bonds prevent the rotation of atoms

around the bond axis which creates 2 different molecules.

• In the “cis” form of the molecule the groups attached to the double bond are on the same side of the double bond.

• In the “trans” form of the molecule the groups are attached on different sides of the double bond.

• Cis and trans goes with the bond NOT THE GROUPS ATTACHED!!

General Rules for Naming Organic Compounds

• the prefix indicates the number of carbon atoms.• the ending indicates the functional groups in the

structure (C=C “ene”, –OH “ol”).• any branches are indicated before the prefix for

the number of carbons in alphabetical order.• below shows the order of different components

in the nameBRANCHES # of C’s BONDS FUNCTIONAL

GROUPS

in alpha order alpha alpha order

(“oic acid” always last)

Aromatics• the organic family which are

derivatives of benzene• Benzene has the molecular

formula C6H6

• The structural formula of benzene consists of a 6-member carbon ring with 3 C=C double bonds.

The Structure of Benzene• Benzene is a planar molecule• The carbon-carbon bonds in benzene are all the

same length which is evidence that the bonds are not true double and single bonds

If the bonds are not true single and double bonds what are they?

• The carbon-carbon bonds in benzene are all 139 pm which is intermediate between the length of a C-C single bond and a C=C double bond (double bonds are shorter).

• This indicates that the electrons that make up the “double bonds” in benzene are actually delocalized (i.e. shared) around all six carbon atoms.

• This arrangement of the electrons is indicated in the LINE DIAGRAM by placing a circle in the centre of the 6-member ring.

• Alternatively, benzene can be represented as below.

Naming Aromatics

Using benzene as the main chain.

1. Identify the groups attached and number accordingly

2. For compounds with 2 groups attached, the following prefixes may be used instead of the numbers; 1,2 = ortho (o), 1,3 = meta (m) and 1,4 = para (p)

para-dichlorobenzenemeta-dichlorobenzeneortho-dichlorobenzene

• When the benzene ring is not the main chain, phenyl is used to indicate a benzene ring as a branch.

Common Names for Aromatics

Alcohols• contain the hydroxyl group (-OH)

• alcohols can be classified by the position of the OH group

1. Primary

• the -OH is at the end of the chain

Ex. 1-butanol CH3CH2CH2CH2OH

2. Secondary

• the -OH is attached to a C with one H

Ex. 2-butanol CH3CH(OH)CH2CH3

3. Tertiary

• the -OH is attached to a C with no H’s

Ex. methyl-2-propanol C(CH3)3OH

Naming Alcohols1. Determine the name of the main chain

containing the hydroxyl group.

2. Remove the ‘e’ on the end of the main chain and add ‘ol’.

3. Indicate the number to which the -OH is bonded to starting at 3 carbons using the same rules as for a double or triple bond.

4. If there are multiple -OH groups indicate this using the appropriate Greek prefix.

Ethers• Contain the R-O-R’ functional group.

Naming

1.The longest carbon chain connected to the O is the base name.

2.Add “oxy” to the end of the prefix for the other carbon chain (e.g methoxy, isopropoxy).

3. Indicate the position of the ether linkage using a number in front of the “oxy branch”.

Peroxides• Contain the R-O-O-R’ functional group.• Very unstable and break down spontaneously to

form the ether and oxygen gas.

Naming

1. list the “yl” forms of the hydrocarbon chains in alpha order, followed by the word peroxide.

Aldehydes and Ketones• Aldehydes and ketones both contain the

carbonyl group (C=O).• In aldehydes, the carbonyl group is attached to

the end carbon.• In ketones, the carbonyl group is attached to a

carbon that is not on the end.• They are considered functional isomers of each

other.

propanal propanone

Naming Aldehydes1. Take the longest chain containing the carbonyl

group, remove the “e” and add “al” as the ending.

2. Any substituents are numbered using the lowest sum.

3. Only number the C=O if it is NOT carbon 1.

Naming Ketones

1. Take the longest chain containing the carbonyl group, remove the “e” and add “one” as the ending.

2. If necessary indicate the position of the carbonyl using the lowest numerical coefficient.

3. Any substituents are numbered so the sum is the lowest.

Carboxylic Acids• Contain the carboxyl functional group

Naming

1. Identify the longest chain containing the carboxyl group, remove the “e” and add “oic” acid.

2.Only use a number for the carboxyl group if it is NOT carbon 1.

Note: “oic acid” always goes last in the name

Esters• Responsible for tastes and odours.• Contain the ester linkage

• Made from an alcohol and a carboxylic acid.

Naming

1. Use the “yl” form of the alcohol proceeded with the “oate” form of the carboxylic acid.

i.e. “alkyl oate”

CH2CH3

methylpropanoate

2-propylethanoate(isopropylacetate)

Amines

• Contain the amino functional group

Types of Amines

1.Primary: Contain 1 carbon chain (2 H’s).

2.Secondary: Contain 2 carbon chains (1 H).

3.Tertiary: Contain 3 carbon chains (no H’s).

Naming Amines1. Determine the longest carbon chain and use it

as the base name.

2. List the other alkyl chains on the N in alpha order with “N” in front of each to indicate that they are on the nitrogen and not the main chain.

3. After the names of the alkyl indicate the position of the amino group and precede the base name with amino.

4. Any other branches go in alpha order after the amino.

N-ethyl-2-aminopentane

trans-N,N-dimethyl-3-amino-3-hexene

N-ethyl-N-methyl-2-amino-5-chloro-3-hexanol

Amides• Contain the amide linkage.

• Structurally similar to esters• This linkage joins amino acids together to create

polypeptides.

Naming Amides• The name has 2 parts.Base Name: 1. The prefix for the number of carbons in the

chain containing the carbonyl.2. Add amide to the end.Before:1. Indicate any groups attached the nitrogen

using N in place of a number.

N-ethylhexanamide

N,N-dimethylbenzamide

Cltrans-N-chloro-N-methylhex-2-enamide

Organic Chemistry

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