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OME General Chemistry
Lecture 11: Introduction to Organic Chemistry
Dr. Vladimir Lesnyak
Office: Physical Chemistry, Erich Müller-Bau, r. 111
Email: [email protected]
Phone: +49 351 463 34907
Outline
1 Bonding of Carbon
Hydrocarbons
2 Alkanes and Cycloalkanes
3 Alkenes and Alkynes
4 Aromatic Hydrocarbons
5 Naming Hydrocarbons
Derivatives of Hydrocarbons
6 Organic Compounds Containing Oxygen
7 Organic Compounds Containing Nitrogen
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Bonding of Carbon
Organic chemistry is the chemistry of compounds containing carbon.
>90% of the compounds in the world are organic compounds.
Carbon forms single, double, and triple bonds to achieve a filled octet:
Carbon can have a tetrahedral, trigonal planar, or linear geometry:
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Covalent Bonds for Elements in Organic Compounds
4
Hydrocarbons
The simplest organic compounds are hydrocarbons, containing only carbon
and hydrogen. 100,000s hydrocarbon molecules exist.
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Alkanes and Cycloalkanes
Alkanes – acyclic saturated hydrocarbons,
cycloalkanes – cyclic saturated hydrocarbons.
The simplest hydrocarbon – methane
molecular formula
space-filling model
structural formula
ball-and-stick model
with bond angle
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Alkanes
General formula: CnH2n+2, n = 1 – CH4, n = 2 – C2H6, n = 3 – C3H8, etc.
Straight-chain or normal alkanes:
methane
ethane
propane
butane
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Alkanes: Conformers
2 parts of an alkane molecule joined by −C−C− single bond are free to spin
around the bond, giving rise to an infinite number of possible 3-dimensional
geometries, or conformations.
The various conformations of a molecule such as butane are conformers of one
another.
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Alkanes
Alkanes constitute a homologous series, a series of compounds in which one
compound differs from a preceding one by a fixed group of atoms.
The boiling and melting points for the straight-chain alkanes
increase with molecular size:
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Nomenclature of Alkanes
This nomenclature is formulated in rules agreed upon by the International Union
of Pure and Applied Chemistry (IUPAC).
First 4 straight-chain alkanes (methane, ethane, propane, and butane) have long
established names. Higher members of the series are named from the Greek words
indicating the number of carbon atoms in the molecule, plus the suffix -ane.
IUPAC Names of the First 10 Alkanes
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Naming Alkanes
Rules for naming the branched-chain alkanes:
1. Determine the longest continuous (not necessarily straight) chain of C atoms in the
molecule. The base name of the branched-chain alkane is that of the straight-chain
alkane.
-heptane
2. Any chain branching off the longest chain is named as an alkyl group. An alkyl group is
an alkane less one H atom. When H atom is removed from an end C atom of a straightchain alkane, the resulting alkyl group is named by changing the suffix -ane of the
alkane to –yl:
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Naming Alkanes
3. The complete name of a branch requires a number that locates the branch on the longest
chain. Number each C atom on the longest chain in the direction that gives the smaller
numbers for the locations of all branches:
3-methylheptane
4. When there are more than 1 alkyl branch of the same kind, this number is indicated by a
prefix, such as di-, tri-, or tetra-, used with the name of the alkyl group. The position of
each group on the longest chain is given by numbers:
3,4-dimethylheptane
3,3-dimethylheptane
5. When there are 2 or more different alkyl branches, the name of each branch, with its
position number, precedes the base name. The branch names are placed in alphabetical
order:
3-ethyl-2-methylpentane
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Constitutional Isomerism and Branched-Chain Alkanes
Constitutional (or structural) isomers – compounds with the same molecular formula
but different structural formulas:
butane
iso-butane
The number of constitutional isomers rapidly increases with the number of carbons
in the series: 3 constitutional isomers of C5H12 (pentanes), 5 of C6H14 (hexanes), and
75 of C10H22 (decanes).
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Cycloalkanes
General formula: CnH2n
First 4 members of the cycloalkane series
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Naming Cycloalkanes
1. Use the cycloalkane name as the parent. Compounds are named as alkylsubstituted cycloalkanes rather than as cycloalkyl-substituted alkanes:
methylcyclohexane
2. Identify and number the substituents. Start numbering at the group that has
alphabetical priority, and proceed around the ring in the direction that gives the
2nd substituent the lower possible number:
1-ethyl-3-methylcyclohexane
1-isopropyl-3-methylcyclohexane
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Hydrocarbons in Nature
Natural gas is a mixture of low molecular weight hydrocarbons made up primarily of
methane CH4, with lesser amounts of ethane C2H6, propane C3H8, and butane C4H10.
Petroleum, or crude oil, is a mixture of alkanes and cycloalkanes with small
amounts of aromatic hydrocarbons.
Fractions from the Distillation of Petroleum
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Crude Oil Refinery
A refinery converts crude oil into gasoline, heating oil, and other organic products
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Reactions of Alkanes
Oxidation
C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(l); ∆Ho = 2220 kJ/mol
Substitution
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Halogen-Containing Compounds
The simplest halogen-containing compounds are the alkyl halides RX, where R is an
alkyl group and X is a halogen. Their common names consist of the name of the alkyl
group + the halogen name with an -ide ending:
CH3Br – methyl bromide
Systematic names consider the halogen atom as a substituent on a parent alkane.
The parent alkane is named in the usual way by selecting the longest continuous
chain and numbering from the end nearer the first substituent, either alkyl or halogen:
1-chloropropane
2-bromo-5-methylhexane trichloromethane
(chloroform)
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Alkenes
Alkenes (olefins) contain −C=C− bond.
General formula: CnH2n.
The simplest alkene is ethylene:
Alkenes typically are much more reactive than alkanes
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Naming Alkenes
The IUPAC name for an alkene is determined by first identifying the longest chain
containing the −C=C− bond, which provides the base name + suffix -ene.
C atoms of this chain are then numbered from the end nearer the −C=C− bond, and
the position of the −C=C− bond is given the number of the 1st C atom of that bond (the
smaller number). This number is written in front of the base name of the alkene.
Branched chains are named the same way as the alkanes.
3-methyl-1-pentene
3-methylcyclopentene
4-butyl-2-nonene
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Geometric Isomerism of Alkenes: cis-trans
π-bonding forces 2 CH2-groups in ethylene to bond so as to give a planar structure
Geometric isomers: atoms are joined to one another in the same way but
differ because some atoms occupy different relative positions in space.
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Reactions of Alkenes
Oxidation
Addition
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Alkynes
Alkynes contain −C≡C− bond.
General formula: CnH2n−2.
The simplest alkene is acetylene (ethyne):
Production
Addition reaction
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Naming Alkynes
Alkynes are named using the IUPAC rules in the same way as the alkenes,
except that the base name is determined from the longest chain that
contains the −C≡C− bond. The suffix for the base name is -yne.
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Aromatic Hydrocarbons
Contain benzene rings:
resonance formula
Molecular orbitals of benzene
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Polycyclic Aromatic Hydrocarbons
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Naming Aromatic Hydrocarbons
benzene as the suffix and the name of the group as the prefix
ethylbenzene
When 2 groups are on the benzene ring, three isomers are possible.
The isomers are distinguished by the prefixes ortho- (o-), meta- (m-), and para- (p-):
o-dimethylbenzene
(o-xylene)
m-dimethylbenzene
(m-xylene)
p-dimethylbenzene
(p-xylene)
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Naming Aromatic Hydrocarbons
3-ethyl-1-methylbenzene
1,3,5-trimethylbenzene
diphenylmethane
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Reactions of Aromatic Hydrocarbons
Substitution
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Organic Functional Groups
Functional group is a reactive portion of a molecule that undergoes predictable reactions
All organic compounds
can be considered as
derivatives of
hydrocarbons, in which
one or more H atoms
are replaced by atoms
other than C to give a
functional group.
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Organic Compounds Containing Oxygen: Alcohols
Alcohols, ethers, aldehydes, ketones, carboxylic acids, esters.
ethanol
(ethyl alcohol)
methanol
(methyl alcohol)
2-propanol
(isopropyl alcohol)
ethylene glycol
glycerol
named similar to hydrocarbons, but the base name is determined from the longest chain
containing C atom with the –OH group attached, + suffix -ol. Position of the –OH group is
indicated by a number preceding the base name:
1-propanol
(propyl alcohol)
4-methyl-2-pentanol
1,3-propanediol
2-methylcyclohexanol
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Phenols
Phenol is the name both of a specific compound (hydroxybenzene, C6H5OH)
and of a family of compounds.
o-chlorophenol
p-methylphenol
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Alcohols
By number of C atoms attached to the C atom with –OH group:
primary alcohol
secondary alcohol
1-butanol
2-butanol
tertiary alcohol
2-methyl-2-propanol
−OR = alkoxy group: −OCH3 – methoxy group, −OCH2CH3 – ethoxy group, etc.
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Hydrogen Bonding in Alcohols
Alcohol boiling points are higher than those
of the corresponding alkanes because of
alcohol–alcohol hydrogen bonding:
Because of hydrogen bonding between
alcohol and water molecules, alcohols
of small molecular mass have unlimited
solubility in water:
Hydrogen bond is an extra-strong dipole–dipole interaction between H atom
covalently bonded to a small, very electronegative atom (F, O, or N) and a lone
pair of electrons on another small, very electronegative atom (F, O, or N).
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Organic Compounds Containing Oxygen: Ethers
water
alcohol
ether
named as derivatives of the longest hydrocarbon chain
dimethyl ether
ethyl methyl ether
diethyl ether
The best-known ether is diethyl ether, often called simply ether, a volatile liquid
used as a solvent and as an anesthetic.
3-methoxy-2-butanol
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Isomers of Alcohols and Ethers
Alcohols and ethers can have the same molecular formula:
C2H6O
ethyl alcohol
dimethyl ether
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Cyclic Ethers
Compounds that contain the oxygen atom in a ring are classified as cyclic
ethers and are often referred to by their common names.
ethylene oxide
tetrahydrofuran
(solvent)
1,4-dioxane
(solvent)
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Organic Compounds Containing Oxygen:
Aldehydes and Ketones
Aldehydes and ketones are compounds containing a carbonyl group:
Aldehyde is a compound containing a carbonyl group
with at least one H atom attached:
methanal
(formaldehyde)
ethanal
(acetaldehyde)
The aldehyde function is usually abbreviated –CHO.
Ketone is a compound containing a carbonyl group with 2 hydrocarbon groups attached.
propanone
(acetone)
The ketone functional group is abbreviated –CO–.
2-butanone
(methyl ethyl ketone)
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Naming Aldehydes and Ketones
Named according to IUPAC rules similar to alcohols:
1. Locate the longest carbon chain containing carbonyl group to get the base
hydrocarbon name.
2. Change the -e ending of the hydrocarbon to -al for aldehydes and -one for ketones.
3. In aldehydes C atom of the –CHO group is always number-1.
4. In ketones the position of –CO– group is indicated by a number before the base
name as the position of –OH in alcohols: the carbon chain is numbered to give the
smaller number for its position.
3-methylbutanal
2-pentanone
(methyl propyl ketone)
cyclohexanone
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Aldehydes of Aromatic Hydrocarbons
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Organic Compounds Containing Oxygen:
Carboxylic Acids
Carboxylic acid is a compound containing the carboxyl group –COOH:
ethanoic acid
(acetic acid)
acyl group
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Naming Carboxylic Acids
Carboxylic acids are named in the IUPAC system by replacing the final -e of the
corresponding alkane name with -oic acid and counting the carboxyl carbon as 1:
propanoic acid
acetyl group
3-methylbutanoic acid
propanoyl group
2-hydroxypropanoic acid
(lactic acid)
benzoyl group
Dicarboxylic acids, which contain 2 groups, are named systematically by
adding the ending -dioic acid to the alkane name:
ethanedioic acid
(oxalic acid)
butanedioic acid
(succinic acid)
pentanedioic acid
(glutaric acid)
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Organic Compounds Containing Oxygen: Esters
Ester is a compound formed from carboxylic acid RCOOH and alcohol R’OH:
Ester names consist of 2 words: 1st is the name of the alkyl group R in the ester group,
2nd is the name of the parent acid, with the family-name ending -ic acid replaced by -ate.
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Esters
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Organic Compounds Containing Nitrogen: Amines
Amines are structurally derived by replacing one or more H atoms of NH3 with
hydrocarbon groups.
primary
amine
secondary
amine
tertiary
amine
When 2 or more alkyl groups are bonded to N atom, they are listed in alphabetical order.
The prefixes di and tri are used to indicate 2 and 3 identical substituents.
methylamine
dimethylamine
ethylmethylpropylamine
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Amines
The aromatic amines use the name aniline. Alkyl groups attached to the N
of aniline are named with the prefix N- followed by the alkyl name:
N-methylaniline
aniline
4-bromoaniline
In a neutralization reaction, an amine acts as a base and reacts with an acid to
form an amine salt. An amine salt is named by replacing the amine part of the
name with ammonium, followed by the name of the negative ion:
methylamine
methylammonium chloride
dimethylamine
dimethylammonium chloride
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Heterocyclic Amines
Heterocyclic amine is a cyclic compound that contains one or more N atoms in the ring.
pyrrolidine
piperidine
pyridine
pyrrole
imidazole
pyrimidine
purine
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Organic Compounds Containing Nitrogen: Amides
Amides are compounds with N directly attached to the carbonyl carbon. They derived
from the reaction of NH3, or of a primary or secondary amine, with a carboxylic acid.
acetic acid
acetamide
N-methylacetamide
N,N-dimethylacetamide
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Classification of Organic Compounds
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