Intro to organic chemistry (orgo)SCH4U – Unit B

Organic Compounds•Organic chemistry: chemistry of carbon

compounds▫Exceptions are oxides of carbon (CO2 and

CO), carbonates, bicarbonates, and cyanides

•Carbon atoms are generally bonded to:▫Each other▫Hydrogen atoms▫Other specific elements (O, N, S, P and

others)

Why study organic chemistry?1. Life is carbon-based. Everyone is made

up of organic compounds. There are more known carbon compounds than any other element.

2. There are several million known organic compounds with ~30,000 more being “discovered” each year.

3. Some common organic compounds include plastics, synthetic and natural fibres, dyes, drugs, pesticides, lighter fluid, and gasoline.

The carbon atom•Carbon has four valence electrons

allowing it to form four bonds with other atoms by sharing its electrons▫This results in a tetrahedral shape

•Carbon forms covalent bonds (sharing of electrons) with carbon atoms

Classification•Since organic compounds are composed

almost entirely of carbon, they are sometimes referred to as hydrocarbons

•Hydrocarbons can be divided into:1. Aliphatics: carbon atoms in an open chain

structure; may have branches, but no rings

2. Alicyclics: carbon atoms arranged in a ring structure

3. Aromatics: structures related to benzene (C6H6)

Classification•Aliphatics can be further categorized into:

1. Alkanes: contains only single bonds (saturated)

2. Alkenes: contains at least one double bond (unsaturated)

3. Alkynes: contains at least on triple bond

IsomersIsomers

Constitutional Isomers

Stereoisomers

Diastereomers Enantiomers

IsomersConstitutional Isomers Stereoisomers

Isomers have same molecular formula

Isomers have same molecular formula

Atoms bonded in a different sequence

Atoms bonded in same sequence

Also known as structural isomers

Differ in 3D orientation of atoms in space

IsomersDiastereomers Enantiomers

Based on a double bond Mirror images of each other around a single carbon atom

Carbon atoms with different types of atoms

At least one carbon atom bonded to four different types of atoms or groups

cis isomer when two identical groups or atoms are on the same sidetrans isomer when two identical groups or atoms are on the opposite side

Diagrams & formulas•A number of different (but related)

diagrams used to express structures in organic chemistry:▫Empirical molecular formula▫Expanded molecular formula▫Complete structural formula▫Condensed structural formula▫Line structural formula▫3D structural formula

Alkanes# of carbons Prefix # of carbons Prefix

1 Meth- 6 Hex-

2 Eth- 7 Hept-

3 Prop- 8 Oct-

4 But- 9 Non-

5 Pent- 10 Dec-

Alkanes•Only single bonds present in the main

chain•General formula is CnH2n+2

•Form a tetrahedral shape▫Note: more on shapes in the next unit

•Create a 109.5° angle between bonds•Considered “saturated” because no other

hydrogen atoms can be added•Always end in “~ane”

Nomenclature•Three parts to organic chemistry

nomenclature:▫Prefix: indicates number, type and location

of branches and/or functional groups (if any)

▫Root: indicates the number of carbon atoms in the main (parent) chain

▫Suffix: indicates the number and location of double or triple bonds (if any) and/or highest priority functional group

Let’s draw alkanes!•Draw all ten basic alkanes and name

them.

Alkyl groups and branching•Each branch of a hydrocarbon is referred

to as an alkyl group (if it contains only C and H)

•Alkyl groups use the same basic roots as alkanes

•Alkyls always end in “~yl”•Also contain a number and hyphen in

front to indicate location on the main carbon chain▫Example: 2-methyl pentane

CH3

CH2CH2

CHCH3

CH3

Alkyl groups and branching•Find the longest carbon chain and assign

sequential numbers to each carbon▫Assign these numbers temporarily starting

from both ends of the carbon chain▫Ultimately will select only one set of

numbers to use•The goal is to use the numbering along

the carbon chain that gives the lowest values assigned to branches

Alkyl groups and branching•Let’s try some! Draw 3-ethyl octane…

CH3 CH2

CH CH2

CH2 CH2

CH2 CH3

CH2CH3

Alkyl groups and branching

Alkyl groups and branching•When there is more than one branch, they

are listed in front of the root and suffix according to alphabetical order of the name of the alkyl group

•Try naming…

•4-ethyl 3-methyl heptaneCH3CH2

CH2CH

CH

CH3

CH2

CH3

CH2CH3

Alkyl groups and branching•If there is more than one of any given

alkyl group▫Indicate all the number for the positions

using commas to separate the numbers, and

▫Use prefixes (on the prefixes – confused yet?) to indicate the number present

Alkyl groups and branching•Try naming…

•5,6-diethyl-3,3,4-trimethyl nonane

CH3

CH2CH2

CH

CH

CH

C

CH2

CH3

CH3

CH3

CH3CH2CH3

CH2

CH3

Alkenes•At least one double bond present in the

main chain•General formula is CnH2n

•Form a trigonal planar shape▫Note: more on shapes in the next unit

•Create a 120° angle between bonds•Considered “unsaturated” because other

hydrogen atoms can be added•Always end in “~ene”

Nomenclature1. Identify and name the longest carbon chain

that CONTAINS THE DOUBLE BOND(S).2. Number the carbons in the chain so that the

two carbons involved in the double bond have the lowest possible numbers.

a) If the double bond is equidistant from both ends, number the chain so that the substituent(s) have the lowest possibly number.

3. Follow same rules for identifying and naming prefixes.

Nomenclature•Try naming this…

•2-ethyl 1-pentene

CH3 CH2

CH2 C

CH2 CH3

CH2

Nomenclature•Now let’s draw 1-butene and 2-butene…

1-butene 2-butene

CH3

CH2 CH

CH2

CH3

CH CH

CH3

Nomenclature•Let’s try a structure with more than one

double bond…

1,3-pentadiene

CH3

CH CH

CH CH2

Nomenclature•Let’s put everything together and name…

•4-ethyl-3,6-dimethyl 1,2,4-octatrieneCH3

CH3

CH3

CH2

CH

CH

C

C

C

CH2

CH2

CH3

Diastereomers•Consider the following compounds…

cis-2-butene trans-2-butene 2-methyl-1-propene

CH3

CH CH

CH3CH3

CH CH

CH3 CH3

C

CH3 CH2

Diastereomers•Not superimposable upon one another•Result from lack of free rotation around

the double bond•Priorities are assigned to the two groups

attached to the carbon atoms on either side of the double bond (starting with the carbon to the left of the double bond) based on atomic number▫Largest atomic number at the first

point of difference has the highest priority

Diastereomers•If two highest priority groups are on the

same side of the double bond (top or bottom)…▫cis configuration

•If two highest priority groups are on the opposite side of the double bond…▫trans configuration

Alkynes•At least one triple bond present in the

main chain•General formula is CnH2n-2

•Form a linear shape▫Note: more on shapes in the next unit

•Create a 180° angle between bonds•Considered “unsaturated” because other

hydrogen atoms can be added•Always end in “~yne”

Nomenclature1. Identify and name the longest carbon chain

that CONTAINS THE TRIPLE BOND(S).2. Number the carbons in the chain so that the

two carbons involved in the triple bond have the lowest possible numbers.

a) If the triple bond is equidistant from both ends, number the chain so that the substituent(s) have the lowest possibly number.

3. Follow same rules for identifying and naming prefixes.

Nomenclature•Try naming this…

•3,4-dimethyl 1-hexyne

CH C CH

CH CH2

CH3

CH3 CH3

Nomenclature•Now let’s draw 1-butyne and 2-butyne…

1-butyne 2-butene

CH3

CH2

C

CH

CH3 C C CH3

Nomenclature•Let’s try a structure with more than one

triple bond…

2,4-hexadiyne

CH3 C C C C CH3

Nomenclature•Let’s put everything together and name…

•4-ethyl-4,5-dimethyl 2,6-octadiyne

CH3 CH2

CH3

C

C

C

CH

C

C

CH3CH3

CH3

Alicyclics•Connected end-to-end forming a ring•Have single and/or double bonds present

in the main chain•General formula is CnH2n

•Can be “saturated” or “unsaturated”•Suffix changes depending on presence of

double bonds•Prefix used is always “cyclo~” before the

root

Nomenclature•Try naming…

cyclobutane cyclo-1-pentenecyclopent-1-ene

CH2

CH2 CH2

CH2

CH

CH2

CH2

CH2CH

Nomenclature•Try drawing…

cyclo-1,4-hexadiene 2,7-diethyl-4-methylcyclo-1,3,5-

heptatriene

CH

CH2 CH

CH

CH2CH

CH3

CH2

CH3CH

C CH

C

CH

CH

CH

CH2

CH3

Aromatics•Based on benzene and the presence of

benzene-like rings•Benzene is a six-carbon ring with three

double bonds▫Cyclo-1,3,5-hexatriene

•However, the electrons in the double bonds are actually spread over the whole molecule = delocalized▫Benzene actually has six identical “1 ½”

bonds

Aromatics•Creates greater stability in the molecule•These “1 ½” bonds do not behave/react

like double bonds•Molecules that have this type of sharing

are referred to as aromatic compounds

Benzene CH

CH

CH

CH

CH

CH

CH

CH

CH

CH

CH

CH

Aromatics•Some common aromatics…

benzene napthalene

antracene

CH

CH

CH

CH

CH

CHCH

CH

CH

C

C

CH CH

CH

CH

CH

CH

CH

CH

C

C

CH CH

C

C

CH CH

CH

CH

CH

Nomenclature1. Number carbons in benzene ring assigning

lowest number to a branch.a. If more than one branch exists, start numbering

at the branch that contains the group with the highest priority (most complex).

2. Name branches attached to the benzene ring, assigning numbers to each branch.

a. If only one branch is present, a number does not need to be assigned.

3. Branches are placed before the root as a prefix.

Nomenclature•Priority of branches on benzene…

Highest priority -OH-NH2-F, -Cl, -Br, -I-CH2CH2CH3-CH2CH3

Lowest priority -CH3

Nomenclature•When benzene has only two branches,

position numbers do not have to be used•Instead, prefixes ortho-, meta-, and para-

replace position numbers

1,2-dimethyl benzeneortho-dimethyl benzene

CH3

CH3

C

CH

CH

CH

CH

C

Nomenclature

1,3-dimethyl benzene1,4-dimethyl benzenemeta-dimethyl benzene para-dimethyl benzene

CH3

CH3

CH

C

CH

CH

CH

C

CH3

CH3

CH

CH

C

CH

CH

C

Nomenclature• IUPAC has retained many of the common names for

aromatics…

Nomenclature•Let’s try naming…

3-ethyl-5-methyl phenol

CH3

OH

CH3CH2

C

CH C

CH

CCH

Nomenclature•Let’s try drawing…

2,6-diethyl-3-methyl benzaldehyde

CH3

OCH

C

C C

C

CHCH

CH2CH3

CH2

CH3

Nomenclature•For use when:

▫Naming compounds with >1 fxn’l group▫Naming compounds with a complicated

substituent

Nomenclature•Try naming…

3-phenyl hexane

CH3

CH2 CH2

CH CH2

CH3C

CH

CHCH

CH

CH

Nomenclature•Try drawing…

4,6-diphenyl 2-octene

C

CH3CH

CH

CH

CH2CH

CH2CH3 CH

CH

CH

CH

CH

C

CH

CH

CH

CH

CH

Up next•That covers the basics of hydrocarbons in

organic chemistry.•Next we will cover functional groups!