Fundamentals of Organic
Chemistry
Topic 10.1
1 2 3 4 bonds
HONC
What is organic chemistry?
• study of carbon, the compounds it makes, and
the reactions it undergoes
• over 16 million carbon-containing compounds
are known
• because the C-C single bond (348 kJ mol-1) and
the C-H bond (412 kJ mol-1) are strong, carbon
compounds are stable
• carbon can form chains and rings
Empirical, molecular & structural formulas
2
• empirical formula
– simplest ratio of
atoms in a
molecule
• molecular formula
– actual number of
each atom in a
molecule
Empirical
Formula
Molecular
Formula
CH4
CH4
CH3
C2H6
CH2O
C6H12O6
CH2
C4H8
CH2
C8H16
structural formula
• unambiguously shows how the atoms are
bonded together
condensed structural formulas
– bonds are omitted, repeated groups put
together, side chains put in parenthesis
• CH3CH2CH2CH2CH2CH3
–or even CH3(CH2)4CH3
• CH3CH(CH3) CH2CH3
condensed
skeletal formula
– not accepted in the IB for answers but often
used in questions
– every vertex or end represents a carbon
– hydrogens are implied
Isomers
• (structural) isomers: compounds with the
same molecular formula but different structure
(arrangement of atoms)
• different isomers are different compounds
• have different physical properties such as
melting point and boiling point
Structural
Formulas
for C4H10O
Isomers
Homologous series/compounds
• related compounds that have the same
functional group (groups of atoms found within
molecules that are involved in the chemical reactions
characteristic of those molecules)
• differ from each other by a CH2 unit
• can be represented by a general formula
– examples:
• CnH2n+2 (alkanes) or CnH2n (alkenes) or…
• have similar chemical properties
• have physical properties that vary in a
regular manner as the number of carbon
atoms increases
– Example: the alkanes
Trends in boiling points of members of a
homologous series
•
•
melting point and
boiling point increase
with more carbon
atoms
Why?
–
intermolecular forces
increase
–
adding a CH2 adds
more electrons
•
this increases the
London dispersion
forces
Alkane
Formula
Boiling
Pt./oC
methane CH4
-162.0
ethane
C2H6
-88.6
propane C3H8
-42.2
butane
C4H10
-0.5
Alkanes
Structural formulas for the isomers of noncyclic alkanes up to C6
• hydrocarbon chains where all the bonds
between carbons are SINGLE bonds
• therefore the chain is said to be saturated with
hydrogen
• draw out and write the structural formulas for all
isomers that can be formed by:
– CH4 C2H6 C3H8 C4H10 C5H12 C6H14
Richard Thornley
2:54
Naming the isomers (IUPAC) of non-cyclic
alkanes up to C6
1. Richard Thornley 3:35
2. Determine the longest carbon chain
–
1
2
3
4
5
6
Use the prefix to denote the number carbons
MethEthPropButPentHex-
Monkeys
Eat
Peeled
Bananas
3. use the suffix “-ane” to indicate that the substance
is an alkane
4. number the carbons in the chain consecutively,
starting at the end closest to a substituent
(groups attached to the main chain)…”most
busy end”
5. name and number the location of each
substituent
– the name of the substituent will be written before the main
chain
– alkyl groups are the simplest substituents (yl ending)
•
•
•
•
CH3 is methyl
C2H5 is ethyl
C3H7 is propyl
C4H9 is butyl
6. use prefixes di-, tri-, tetra-, to indicate when
there are multiple side chains of the same type
7. use commas to separate numbers and hyphens
to separate numbers or letters.
8. name the side chains in alphabetical order
• How about C5H12? The isomers are:
Pentane
2-methyl-butane 2,2-dimethyl propane
Nomenclature Practice
Name this compound
CH3
H3C1 2
Cl
3 4
5
CH3
9 carbons = nonane
6
7
8
H3C9
Step #1: For a branched hydrocarbon, the longest
continuous chain of carbon atoms gives the root name
for the hydrocarbon
Nomenclature Practice
Name this compound
CH3
H3C1 2
Cl
3 4
5
CH3
6
9 carbons = nonane
CH3 = methyl
7
8
chlorine = chloro
H3C9
Step #2: When alkane groups appear as substituents, they are named
by dropping the -ane and adding -yl.
Nomenclature Practice
Name this compound
CH3
H3C1 2
Cl
3 4
5
9 carbons = nonane
CH3
6
CH3 = methyl
7
chlorine = chloro
8
H3C9
1
9 NOT
9
1
Step #3: The positions of substituent groups are
specified by numbering the longest chain of carbon
atoms sequentially, starting at the end closest to the
branching.
Nomenclature Practice
Name this compound
CH3
H3C1 2
Cl
3 4
5
CH3
9 carbons = nonane
6
CH3 = methyl
7
8
chlorine = chloro
H3C9
2-chloro-3,6-dimethylnonane
Step #4: The location and name of each substituent are
followed by the root alkane name. The substituents are
listed in alphabetical order (irrespective of any prefix),
and the prefixes di-, tri-, etc. are used to indicate
multiple identical substituents.
Alkenes and Alkynes
Structural formulas for the isomers of straight
chains
• alkenes have a double bond between two or more of the
carbons (alkynes have a triple bond)
• the carbons are unsaturated, not as many hydrogens
because double bonds are present
• CnH2n
•
draw out and write the structural formulas for all isomers that can be
formed by each
Richard Thornley 10.1.7 (1:37)
– C2H4
– C3H6
– C4H8
– C5H10
– C6H12
Naming the isomers (IUPAC) of straight chain
alkenes or alkynes up to C6
1. suffix changes to “-ene” for alkenes and “yne” for alkynes
2. when there are 4 or more carbon atoms in a
chain, the location of the double/triple
bond is indicated by a number
3. begin counting the carbons closest to the
end with the double or triple bond
– numbering the location of the multiple
bonds takes precedence over the location
of any substituents
but-1-ene
but-2-ene
methyl propene
Naming Practice!!!
CH2
CH3 CH2 C
CH2 CH3
CH2 C
CH3
CH3
choose the correct ending
ene
CH2
CH3 CH2 C
CH2 CH3
CH2 C
CH3
CH3
determine the longest carbon chain with
the double bond
ene
CH2
CH3 CH2 C
CH2 CH3
CH2 C
CH3
CH3
assign numbers to each carbon
ene
CH2
CH2 CH3
1
CH3 CH2 C
2
5
CH2 C
3
4
6
CH3
CH3
assign numbers to each carbon
ene
CH2
CH2 CH3
1
CH3 CH2 C
2
5
CH2 C
3
4
6
CH3
CH3
attach prefix (according to # of carbons)
1-hexene
ene
CH2
ethyl
CH2 CH3
1
CH3 CH2 C
2
5
CH2 C
3
4
CH3
6
CH3
methyl
methyl
determine name for side chains
1-hexene
CH2
ethyl
CH2 CH3
1
CH3 CH2 C
2
5
CH2 C
3
4
CH3
6
CH3
methyl
methyl
attach name of branches alphabetically
2-ethyl-4-methyl-4-methyl-1-hexene
CH2
ethyl
CH2 CH3
1
CH3 CH2 C
2
5
CH2 C
3
4
CH3
6
CH3
methyl
methyl
group similar branches
2-ethyl-4-methyl-4-methyl-1-hexene
CH2
ethyl
CH2 CH3
1
CH3 CH2 C
2
5
CH2 C
3
4
CH3
6
CH3
methyl
methyl
group similar branches
2-ethyl - 4,4 - dimethyl hex-1-ene
CH3 CH
CH2
propene
CH3 CH
CH3
CH3
CH
CH3
CH
C
CH3
CH CH3
2,4-dimethyl pent-2-tene
but-2-ene
CH3
CH2 CH
C
CH3
CH2 CH3
CH3
CH3
C
CH
CH2
a) 3,3-dimethyl pent-1-ene
C
C
CH
CH3
b) same
CH3
CH3
CH2
CH
CH3
CH3
c) 4,5 dimethyl hex-2-ene