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
Isomers
Isomers
Constitutional
Isomers
Stereoisomers
Diastereomers
Enantiomers
Isomers
Constitutional 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
Isomers
Diastereomers
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 side
trans 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
CH2
H3C
CH
CH2
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…
CH2 CH3
H3C
CH2
CH
H3C
CH2
CH2 CH2
CH2
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…
H3C
CH3
CH2
HC
• 4-ethyl 3-methyl heptane
H3C
CH
CH2
CH2
CH2
CH3
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
CH3
• Try naming…
H2C
CH3
CH3
CH2
H3C
CH
CH2
CH
CH
C
CH3
CH2
H2C
H3C
CH3
• 5,6-diethyl-3,3,4-trimethyl nonane
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”
Nomenclature
1. 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…
H3C
CH2
CH2
CH2
• 2-ethyl 1-pentene
C
CH2
CH3
Nomenclature
• Now let’s draw 1-butene and 2-butene…
CH3
CH2
CH2
H3C
1-butene
CH
CH
CH
H3C
2-butene
Nomenclature
• Let’s try a structure with more than one double
bond…
CH
CH
CH
H3C
1,3-pentadiene
CH2
Nomenclature
• Let’s put everything together and name…
CH3
CH3
H2C
CH2
H3C
CH
CH2
C
CH
C
C
CH3
• 4-ethyl-3,6-dimethyl 1,2,4-octatriene
Diastereomers
• Consider the following compounds…
CH3
CH
CH
CH
H3C
CH3
CH
C
CH3
H3C
cis-2-butene
H3C
trans-2-butene
CH2
2-methyl1-propene
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”
Nomenclature
1. 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…
HC
CH3
C
HC
CH
• 3,4-dimethyl 1-hexyne
H3C
CH2
CH3
Nomenclature
• Now let’s draw 1-butyne and 2-butyne…
CH2
H3C
C
H3C
C
C
CH
1-butyne
2-butene
CH3
Nomenclature
• Let’s try a structure with more than one triple
bond…
H3C
C
C
C
2,4-hexadiyne
C
CH3
Nomenclature
• Let’s put everything together and name…
CH3
H3C
CH2
CH
C
C
C
C
C
CH3
H3C
• 4-ethyl-4,5-dimethyl 2,6-octadiyne
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…
CH2
H2C
CH2
H2C
CH2
cyclobutane
HC
CH2
CH
CH2
cyclo-1-pentene
cyclopent-1-ene
Nomenclature
CH3
H2C
• Try drawing…
CH2
CH
HC
C
HC
CH
CH
CH2
CH
C
CH
H3C
CH2
cyclo-1,4-hexadiene
CH
CH
2,7-diethyl-4-methyl
cyclo-1,3,5-heptatriene
CH3
Aromatics
• Based on benzene and the presence of benzenelike 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
CH
Benzene
CH
HC
CH
HC
CH
HC
CH
HC
CH
CH
CH
Aromatics
• Some common aromatics…
CH
CH
HC
CH
HC
CH
CH
HC
C
CH
HC
C
CH
CH
CH
benzene
CH
napthalene
CH
antracene
CH
CH
HC
C
C
CH
HC
C
C
CH
CH
CH
CH
Nomenclature
1. 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 parareplace position numbers
CH3
C
1,2-dimethyl benzene
ortho-dimethyl benzene
CH3
HC
C
HC
CH
CH
Nomenclature
CH3
C
CH3
HC
CH
HC
CH
C
HC
CH
C
HC
C
CH
CH3
CH3
1,3-dimethyl benzene
1,4-dimethyl benzene
meta-dimethyl benzene
para-dimethyl benzene
Nomenclature
• IUPAC has retained many of the common names for aromatics…
Nomenclature
CH2
• Let’s try naming…
CH
H3C
C
CH
CH
3-ethyl-5-methyl phenol
C
C
OH
CH3
Nomenclature
• Let’s try drawing…
H3C
CH2
C
H3C
O
C
CH2
C
C
CH
CH
CH
2,6-diethyl-3-methyl benzaldehyde
CH3
Nomenclature
• For use when:
▫ Naming compounds with >1 fxn’l group
▫ Naming compounds with a complicated
substituent
Nomenclature
• Try naming…
H3C
CH2 CH2
CH
CH
HC
3-phenyl hexane
C
CH3
CH
CH
CH2
CH
Nomenclature
• Try drawing…
CH
HC
CH
HC
C
CH
H3C
4,6-diphenyl 2-octene
CH2
CH
CH
CH
CH2
C
CH
HC
CH
HC
CH
CH
CH3
Up next
• That covers the basics of hydrocarbons in
organic chemistry.
• Next we will cover functional groups!