Organic Chemistry

1
Organic Chemistry

• The Study of the Compounds of Carbon

2
Carbons Place on the Periodic Table
3
Unique Properties of Carbon

• Carbon has a modest electronegativity and forms
  primarily covalent bonds
• Carbon is capable of catenation (bonding to
  itself)
• Carbon has four valence electrons and octet
  requirements require it to bond four times
• Depending on bonding (presence of single, double,
  or triple bonds) carbon compounds can exhibit
  tetrahedral, trigonal planar or linear geometries
• Though carbon and hydrogen form the backbone
  structure, carbon can also bond to other
  elements, like O and N, which are called
  heteroatoms

4
Bond Polarities

• Electronegativity values for some elements found
  in organic compounds are as follows
• C 2.5 H 2.1 O 3.5
• N 3.0 F 4.0 Cl 3.0
• Obviously C - C bonds are nonpolar
• C - H bonds are essentially nonpolar
• Electronegativity differences between carbon and
  O, N, Cl and F suggest that when carbons bonds
  with one of those elements the bonds will be polar

5
Carbon Skeletons

• Since carbon bonds four times, it can assume a
  very complex set of bonding arrangements.
• Single bonded carbons can rotate relative to one
  another, so arrangements can be represented in
  different ways, as shown below

6
Consider the Diversity of Carbon Compounds
Single Bonds
Double Bonds
Rings
7
Hydrogen Skins
8
Hydrocarbon Representations
Expanded Structure
CH3CH2CH2CH2CH2CH3
Condensed Structure
Bond-line Representation
C6H14
Molecular Formula
9
Isomers
Note that for the formula C6H14, several possible
structures exist. These alternate forms are
called structural isomers. Note that each of
these isomers is a different compound with
different properties - and a different name.
CH3
CH3CH2CH2CH2CH2CH3
CH3CH2CHCH2CH3
CH3
CH3
CH3CHCH2CH2CH3
CH3CHCHCH3
CH3
One more isomer exists. Can you suggest what it
is?
10
Hydrocarbon Nomenclature
PREFIX ROOT SUFFIX
Number of C atoms
Roots
meth-
1
Note that beginning with 5 Cs, the roots are
numerical
eth-
2
prop-
3
but-
4
pent-
5
hex-
6
hept-
7
oct-
8
non-
9
dec-
10
11
Rules for Naming Alkanes
Note that alkanes contain only single bonds and
have the generalized formula CnH2n2
Rules for Naming Organic Compounds
12
Alkane Nomenclature Examples
Suggest appropriate names for the following
CH3
Br
CH3CHCH2CH2CH3
CH3CHCHCH2CH3
CH3
CH3
Cl
CH2CH3
CH3
CH3CHCH2CHCHCH3
CH3CH2CHCHCH2CHCH3
CH3
Br
13
Alkane Nomenclature Examples (II)
Suggest appropriate names for the following
Br
CH3
CH3CHCHCH2CH3
CH3CHCH2CH2CH3
CH3
2-methylpentane
2-bromo-3-methylpentane
CH3
Cl
CH2CH3
CH3
CH3CHCH2CHCHCH3
CH3CH2CHCHCH2CHCH3
CH3
Br
3-chloro-2,4-dimethylhexane
4-bromo-5-ethyl-2-methylheptane
14
Alkane Nomenclature (III)
Suggest reasonable structures for the following
names
5-bromo-2,2-dimethyloctane
3-ethyl-2,3,4-trimethylhexane
15
Alkane Nomenclature (IV)
Suggest reasonable structures for the following
names
5-bromo-2,2-dimethyloctane
4-ethyl-2,3,5-trimethylheptane
CH3
Br
CH3
CH2H3
CH3CCH2CH2CHCH2CH2CH3
CH3 CH CH CH CH CH2 CH3
CH3
CH3
CH3
16
Cycloalkane Representations
cyclopropane
cyclobutane
17
Cycloalkanes
Cycloalkanes contain rings, and have the
generalized formula CnH2n Cycloalkanes are
usually represented by polygons, as shown below
Cyclopropane
Cyclobutane
Cyclopentane
Cyclohexane
18
Cycloalkane Nomenclature
When only one substituent is on the ring,
numbering is not necessary.
Chlorocyclohexane
When two or more substituents are present, the
substituent that is first alphabetically is
assumed to be on carbon one, and the others are
numbered, clockwise or counter-clockwise to give
the smallest number arrangement.
1-chloro-3-methylcyclohexane
19
Alkenes

• Alkenes contain at least one double bond.
• Their molecular formula is CnH2n
• The double-bonded carbons have trigonal planar
  
• geometries.
• An expanded structure for ethene, the simplest
  alkene,
• is shown below

H
H
C
C
116.6o
H
H
121.7o
20
Alkenes (II)
Note that there is no rotation around a double
bond, in contrast to single bonds. This factor
leads to the possibility of cis-trans, or
geometric, isomerism. When atoms are bonded to
double-bonded carbons, they are constrained to
remain in the same position. For example, two
kinds of 2-butene exist as is shown below
CH3
CH3
H
CH3
C
C
C
C
H
H
CH3
H
trans-2-butene
cis-2-butene
CH3 groups are trans, or opposite one another
CH3 groups are cis, or same side of double bond
21
Alkene Nomenclature

• The double bond plays a prominent role in alkene
  nomenclature. Despite whatever else is present,
  the carbon chain is numbered from whichever end
  is closest to the double bond.
• When a double bond is present, the name ending is
  changed from -ane to -ene.

22
Alkene Nomenclature (II)
CH2CH3
CH3
Example 1
C
C
H
H
This compound is called 2-pentene, or more
correctly, cis-2-pentene, since the continuing
carbon chains are situated on the same side of
the double bond. Generally, if sufficient
structure information is provided, you should
assign a cis or trans designation to the name
23
Alkene Nomenclature (III)
Other rules we have learned also apply to
alkenes, except that the double bond dictates the
direction of chain numbering. For example
H
CH3CH2
Br
C
C
CH2CHCH3
H
trans-6-bromo-3-heptene
Note that the double bond determines chain
numbering, not the bromo group.
24
Alkene Nomenclature (IV)
Provide a complete, correct name for the
following
Br
CH2CCH3
CH3
C
C
CH3
H
H
25
Alkene Nomenclature (IV)
Provide a complete, correct name for the
following
Br
CH2CCH3
CH3
C
C
CH3
H
H
cis-5-bromo-5-methyl-2-hexene
26
Cycloalkenes
Cycloalkenes, which have a molecular formula of
CnH2n-2, share many characteristics of alkenes,
however, in order to form rings, the double bond
generally must be in the cis form. When naming a
cycloalkene, it is understood that the
double-bonded carbons are numbered 1 and 2.
Examples
Cyclohexene
3-methylcyclohexene
27
Alkynes

• Hydrocarbons containing a triple bond are called
  alkynes, and have molecular formulas of CnH2n-2.
• The triple bonded carbons exhibit linear
  geometries, with bond angles of 180o.
• This geometry prevents them from forming rings.
• Nomenclature for alkynes is completely analogous
  to the method for alkenes.

28
Aromatic Hydrocarbons

• Aromatic hydrocarbons are ring structures with
  multiple double bonds. The double bonds are
  conjugated, alternating double and single bonds.
• Aromatic hydrocarbons have molecular formulas
  approaching CnHn.
• These structures are planar, with all ring
  carbons exhibiting a trigonal planar geometry,
  and a high degree of resonance.
• A number of aromatics are notorious carcinogens

29
Aromatic Nomenclature
30
Aromatic Nomenclature (II)
Nomenclature for aromatics is performed much like
other cyclic compounds. If only one substituent
is present, numbering is unnecessary If one of
the common names, such as phenol, is used, it is
understood that the substituent is on carbon 1.
Other substituents present are numbered or given
a special designation used in aromatic
chemistry. In general, substituents are numbered
by counting clockwise or counterclockwise to
produce the lowest numbering pattern.
31
Aromatic Nomenclature (II)

• Nomenclature for aromatics is performed much like
  other cyclic compounds.
• If only one substituent is present, numbering is
  unnecessary
• If one of the common names, such as phenol, is
  used, it is understood that the substituent is on
  carbon 1. Other substituents present are either
  numbered or given a special designation used in
  aromatic chemistry.
• 1-2 substitution is called ortho
• 1-3 substitution is called meta
• 1-4 substitution is called para

32
Aromatic Nomenclature (III)
Examples
3-chloroaniline
4-bromotoluene
2,4-dimethylphenol
or meta-chloroaniline
or para-bromotoluene
33
Hydrocarbon Chemistry

• Hydrocarbons are generally derived from natural
  sources, particularly petroleum.
• The most plentiful compounds in petroleum are
  alkanes.
• A number of reactions can be used to convert one
  type of hydrocarbon into another.
• Organic compounds are much more reactive when
  heteroatoms, N and O, are present.

34
Alkanes

• Alkanes are generally considered to be
  unreactive.
• They are commonly combusted as gasoline, diesel,
  kerosene, etc.
• They can also be reacted with the halogens, e.g.
  Cl2 and Br2, to form halogenated forms.
• The halogenated forms can be used to produce
  other compounds.

35
Alkenes

• The double bond in alkenes makes them much more
  reactive than alkanes.
• The pi electrons in the double bond are
  relatively loosely held, and the double bond is
  subject to attack by substances attracted to
  negative charge (electrophiles).
• Generally, substances are added to the doubly
  bonded carbons, and the double bond is lost.
• Ethylene and propylene are heavily used to
  produce polymers polyethylene and polypropylene.

36
Alkynes

• Alkynes have two pi bonds, and react much like
  alkenes, except that stoichiometrically they tend
  to react twice as much.
• The most common alkyne, acetylene, is capable of
  participating in unusual reactions with strong
  bases, and it combusts at very high temperature,
  which makes it ideal for welding torches.

37
Aromatic Compounds

• Although aromatic compounds contain double bonds,
  they do not react like alkenes, because the loss
  of double bonds would eliminate their stabilizing
  resonance.
• Instead, aromatic compounds tend to undergo
  substitution reactions, where other substances
  replace hydrogen atoms on the ring carbons.
• A number of aromatic hydrocarbons are produced as
  pollutants when other hydrocarbons are burned.

38
Functional Groups

• When organic compounds contain elements other
  than carbon, called heteroatoms, such as oxygen
  and nitrogen, the structural units containing the
  heteroatoms are called functional groups.
• These functional groups add unique chemical
  characteristics to the compound, which makes them
  very important in biological applications.

39
Alcohols

• When a carbon atom is bonded to an -O-H group,
  often designated as R-O-H, where R is used as a
  general designation for a carbon group, the
  molecule is called an alcohol.
• The -OH group is very polar, and most small
  alcohols have high boiling points and good water
  solubility.
• Besides simple alcohols, alcohols are found
  biologically in carbohydrates and various
  metabolites.

40
Alcohol Nomenclature

• Alcohols often have common trivial names, but
  IUPAC nomenclature rules suggest that the alcohol
  name contain the -ol suffix.
• The alcohol group is considered higher priority
  than any carbon-containing group, and the chain
  should be numbered from whichever end is closest
  to the alcohol group.
• Other groups are named and numbered as shown
  previously

41
Alcohol Nomenclature (II)
Examples
Ethyl alcohol (trivial name)
CH3CH2-OH
Ethanol (IUPAC name)
4-chloro-2-pentanol
6-bromo-4-methyl-2-hexanol
OH
3-methylcyclohexanol
CH3
42
Ethers

• Another oxygen-containing functional group is the
  ether. The ether group, sometimes designated as
  R1-O-R2, contains an oxygen bridge between two
  carbon atoms.
• Ethers, unlike alcohols, do not participate in
  hydrogen bonds, and are not considered polar.
• Ethers, which are important medical and
  industrial chemicals, are not commonly found
  naturally in biological systems.

43
Ether Nomenclature

• Although IUPAC recommends a method for naming
  ethers, we will only focus on a trivial method
  that is in common use.
• With this method, the two carbon-containing
  groups connected by the oxygen are listed
  alphabetically, followed by the name ether.

44
Ether Nomenclature (II)
Examples
CH3-O-CH2CH3
Ethyl methyl ether
O
CH3
Cyclohexyl methyl ether
CH3CH2-O-CH2CH3
Diethyl ether
Diethyl ether was used for years as an anesthetic
until it was replaced due to safety
considerations.
45
Carbonyl Groups

• The carbonyl group contains a carbon-oxygen
  double bond. This functional group can be found
  in the interior of a carbon chain, where it is
  called a ketone, or on a terminal carbon, where
  it called an aldehyde.
• A commonly used representations of ketones and
  aldehydes look as follows

Ketone
Aldehyde
46
Carbonyl Groups (II)

• Carbonyl groups, particularly aldehydes, are very
  reactive, and appear in many biological
  compounds.
• Like alcohols, carbonyl groups are found in
  carbohydrates, and they are observed during many
  metabolic processes
• These compounds are moderately polar, and the
  smaller ketones and aldehydes are water soluble.
• A number of ketones have common names, such as
  acetone and methyl ethyl ketone (MEK), and are
  widely used industrial solvents.

47
Ketone Nomenclature

• When a ketone is present in a compound, it is
  considered higher priority than anything
  discussed thus far, and the chain is numbered
  from whichever end is closest to the ketone. If
  an alcohol is also present, it is given a number
  and is called a hydroxy group.
• When a ketone is present, the suffix for the name
  is changed to -one.

48
Ketone Nomenclature (II)
Examples
Acetone (trivial name)
2-propanone (IUPAC name)
Methyl ethyl ketone (trivial name)
2-butanone (IUPAC name)
5-hydroxy-2-methyl-3-hexanone
49
Aldehyde Nomenclature

• When an aldehyde is present in a compound, it is
  considered higher priority than anything
  discussed thus far, and the chain is numbered
  from aldehyde end. The aldhyde group is
  understood to be on the terminal carbon, so it
  needs no number. If ketones are also present,
  they are called oxo groups and are given a
  number.
• When an aldehyde is present, the suffix of the
  name is changed to -al.
• Remember, aldehydes can be represented as

50
Aldehyde Nomenclature (II)
Examples
Formaldehyde (trivial name)
Methanal (IUPAC name)
3-oxobutanal
5-chloro-2-hydroxy-4-oxohexanal
51
Carboxylic Acids

• Carboxylic acids have the generalized formula
• The carboxyl name is a contraction of carbonyl
  and hydroxyl group names, which are both present.
• The hydrogen on the hydroxyl group is acidic, and
  carboxylic acids are notable for their acidic
  behavior.
• Carboxylic acids are found in many biological
  compounds, most notably amino acids.

52
Carboxylic Acid Nomenclature

• The carboxylic acid structure requires that this
  functional group be on a terminal carbon.
• The carboxyl group has higher priority than any
  other functional group, and if it is present, it
  is understood to be on carbon number 1, and the
  chain is numbered away from it.
• Other groups present are numbered appropriately,
  and the names suffix is changed to -oic,
  followed by the word acid.
• There are many trivial names, such as acetic acid
  that are commonly used.

53
Carboxylic Acid Nomenclature (II)
Examples
Acetic acid (trivial name)
Ethanoic acid (IUPAC name)
Gamma-hydroxybutyric acid or GHB
(trivial name)
4-hydroxybutanoic acid
4,5-dichloro-2-methylhexanoic acid
54
Amines

• Amines act as bases in organic chemistry.
• They contain the amino functional group
• R-NH2
• These compounds are notable for their basic
  nature and strong odors.
• Nitrogen-containing compounds, or amines, are
  found in a variety of biological compounds
  including amino acids and nucleic acids.

55
Amine Nomenclature

• Amines are commonly named by referring to the
  alkyl group attached to them, followed by the
  word amine.
• In IUPAC, or systematic, nomenclature, the amine
  is numbered from which ever end of the chain is
  closest.
• The final e of the name is replaced by the
  suffix -amine.
• If a higher priority group is present, the amine
  is called an amino group and given a number.
  All of the oxygen-containing functional groups
  are considered higher priority.
• Finally, though we wont cover them, amines exist
  where more than one carbon group is attached to
  the nitrogen atom.

56
Amine Nomenclature (II)
Examples
Isopropyl amine (trivial name)
2-propanamine (IUPAC name)
3-amino-1-butanol
Alanine (amino acid)
2-aminopropanoic acid