Transcript CHEMISTRY Lecture 10 Slides - International University of Sarajevo

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Lecture 10:
Organic Compounds
Spring 2014
Course lecturer :
Jasmin Šutković
29 th April 2014
Contents
International University of Sarajevo
1. Functional classes and types of Org. Compounds
Alkanes
Alkenes
Alkynes
Aromatic compounds
2. Isomeric variations of Organic compounds
3. Reactivity of Organic compound
4. Chemical reactions of Organic Compounds
Substitution
Addition
Elimination
Functional Groups and Classes
of Organic Compounds
 Organic compounds are covalent compounds composed
primarily of carbon and hydrogen
 Carbon is unique among the elements in its ability to
catenate, forming long chains and cyclic structures in a
wide variety of compounds
 Functional groups are structural units that determine
the chemical reactivity of a molecule under a given set of
conditions
– Can consist of a single atom or a group of atoms
– Organic compounds are classified into several major
categories based on the functional groups they contain
Organic Compounds main
classes
Organic compounds
functional groups
ALKANES
CnH2n+2
CH4
C2H6
C3H8
C4H10
etc.
C2H6
ethane
H
H
H—C—C—H
H
Single bond…
H
• sp3 conformation
•bond angles = 109.5o
•σ-bonds (sigma)
H
H
C
HH
Rotation about C--C (conformations)
C
H
H
C3H8
propane
H H H
H C C C H
H H H
CH3CH2CH3
projection formula
partially condensed formula
C4H10
butane(s)
H H H H
H C C C C H
H H H H
CH3CH2CH2CH3
H
H C H
H
H C
H
C
H
CH3
CH3CHCH3
H
C H
H
projection
partially condensed
stick formulas
Two isomers of butane C4H10:
CH3CH2CH2CH3
n-butane
CH3
CH3CHCH3
isobutane
Isomers are different compounds that
have the same molecular formula
Alkane
name
CH4
methane
C 2H 6
ethane
C 3H 8
propane
C4H10
butanes
C5H12
pentanes
C6H14
hexanes
C7H16
heptanes
C8H18
octanes
C9H20
nonanes
C10H22
decanes
…….
C20H42
eicosanes
each new common
name requires a
new prefix…
hexanes C6H14
common names
CH3CH2CH2CH2CH2CH3
n-hexane
CH3
CH3CHCH2CH2CH3
isohexane
IUPAC nomenclature (Geneva, 1920)
NAMES OF RADICALS (ALKYL GROUPS):
CH3-
“methyl”
CH3Cl methyl chloride
CH3OH methyl alcohol, etc.
CH3CH2- “ethyl”
CH3CH2CH2- “n-propyl”
CH3CHCH3
|
“isopropyl”
n-propyl bromide
CH3CH2CH2Br
BrCH2CH2CH3
CH3
CH2CH2Br
CH3
CH3CHBr
CH3
CHBr
CH3
isopropyl bromide
CH3CHCH3
Br
n-butyl chloride
CH3CH2CH2CH2Cl
CH3CH2CH2CH2
Cl
ClCH2CH2CH2CH3
sec-butyl chloride
CH3CHCH2CH3
Cl
CH3CH2CHCH3
Cl
CH3
CH3CH2CHCl
IUPAC rules for naming alkanes:
1.
parent chain = longest continuous carbon chain  “alkane”.
2.
branches on the parent chain are named as “alkyl” groups.
3.
number the parent chain starting from the end that gives you the lower
number for the first branch (principle of lower number).
4.
assign “locants” to the alkyl branches.
5.
if an alkyl group appears more than once use prefixes: di, tri, tetra, penta…;
each alkyl group must have a locant!
6.
the name is written as one word with the parent name last. The names and
locants for the alkyl branches are put in alphabetic order (ignore all prefixes
except iso) separating numbers from numbers with commas and letters from
numbers with hyphens.
fossil fuels:
natural gas
petroleum
coal
petroleum is a complex mixture of hydrocarbons
1. solvents
2. fuels
3. raw materials for chemical syntheses
separated into fractions by fractional distillation in an oil refinery
Alkenes
CnH2n
“unsaturated” hydrocarbons
C2H4 ethylene
H
H
C C
H
H
Functional group = carbon-carbon double bond
sp2 hybridization => flat, 120o bond angles
σ bond & π bond => H2C=CH2
C3H6 propylene
C4H8 butylenes
CH3CH=CH2
CH3CH2CH=CH2
α-butylene
1-butene
CH3CH=CHCH3
β-butylene
2-butene
CH3
CH3C=CH2
isobutylene
2-methylpropene
There are two 2-butenes:
H
H
C C
H3C
CH3
cis-2-butene
“geometric isomers”
H
CH3
C C
H3C
H
trans-2-butene
(diastereomers)
CIS /TRANS or E-Z systems
E/Z system is now recommended by IUPAC for the
designation of geometric isomerism.
1. Use the sequence rules to assign the higher priority * to
the two groups attached to each vinyl carbon.
2. *
*
*
*
(Z)- “zusammen”
together
(E)- “entgegen”
opposite
Nomenclature of alkenes (basic steps):
1. Parent chain = longest continuous carbon chain that
contains the C=C.
2. alkane => change –ane to –ene prefix a locant for the
carbon-carbon double bond using the principle of lower
number.
2. If a geometric isomer, use E/Z (or cis/trans) to indicate
which isomer it is.
H3C
CH2CH3
*
C C *
H
CH3
H3C
Cl
*
C C
H
Br
*
(Z)-3-methyl-2-pentene
(3-methyl-cis-2-pentene)
(E)-1-bromo-1-chloropropene
Alkynes CnH2n-2
C2H2
H—C  C—H
sp configuration
Main representative is Acetylene OR Ethyne
Example :
C3H4
CH3CCH
propyne OR methyl-acetylene
Nomenclature:
common names: “alkylacetylene”
•IUPAC: parent chain = longest continuous carbon chain that
contains the triple bond.
•add -yne
•prefix locant for the triple bond, etc.
CH3CH2CCCH3
2-pentyne
ethylmethylacetylene
“terminal” alkynes have the triple bond at the end of the chain:
CH3CH2CCH
1-butyne
ethylacetylene
CH3
HCCCHCH2CH3
3-methyl-1-pentyne
sec-butylacetylene
Aromatic compounds
 Aromatic compounds are compounds
which contain a benzene ring in their
molecules
 Benzene C6H6
 Methylbenzene C7H8
 Ethylbenzene C8H10
Benzene
The six carbon-carbon bonds in benzene
are identical, intermediate in length
between double and single bonds
Sigma bonding in benzene
 Six carbon atoms joined to form a hexagonal
planar ring.
 Each carbon has four valence electrons!
 One of these is used to form a bond with a
hydrogen atom.
 Two other electrons are used to form sigma
bonds with the carbon atoms on either side.
Range and scope of
aromatic chemistry
 Pharmaceutical compounds, e.g. Morphine
 Herbicides (Herbicides, also commonly known as weedkillers, are
pesticides used to kill unwanted plants)
 Detergents (e.g. Sodium dodecylbenzenesulfonate- It is a
major component of laundry detergent )
 Dyes
Aromatic compounds and
cancer
 Some aromatic compounds are
carcinogenic, e.g. Benzene
 However, not all aromatic compounds are
carcinogenic; aspirin is an example
Organic compounds
groups :
1. First family is the hydrocarbons, which include alkanes, with
the general molecular formula CnH2n+2 where n is an integer;
alkenes represented by CnH2n; alkynes represented by CnH2n–2;
and arenes (CnHn)
2. Second family is the halogen-substituted alkanes, alkenes,
and arenes, which include the alkyl halides and aryl halides
3. Third family is the oxygen-containing organic compounds,
which are divided into two main types:
a. Those that contain at least one C–O single bond, which
include alcohols, phenols, and ethers
b. Those that contain a carbonyl group (> CO), which include
aldehydes, ketones, and carboxylic acids
4. Fourth family is the carboxylic acid derivatives; these are
compounds in which the H atom on the –CO2H functional
group is replaced either by an alkyl group, producing an ester,
or by an amine, forming an amide
5. Fifth family is the nitrogen-containing organic compounds;
these include amines, nitriles (which have a CN triple bond)
and nitro compounds (which contain the NO2 group)
Isomeric Variations in
Structure
• Isomers are different compounds that have the same
molecular formula
• Three main types of isomers:
1. Conformational
2. Constitutional (structural)
3. Stereoisomers
Conformational Isomers
• The C–C single bonds in alkanes are formed by the
overlap of an sp3 hybrid orbital on one carbon atom with
an sp3 hybrid orbital on another carbon atom, forming a 
bond (sigma)
• Differences in three-dimensional structure resulting from
rotation about a  bond are called differences in
conformation, and each different arrangement is called a
conformational isomer
• Differences between the conformations are
depicted in drawings called Newman projections
– A Newman projection represents the view along a
C–C bond axis, with the carbon that is in front shown
as a point and the carbon that is bonded to it shown
as a circle
– In one extreme, the eclipsed conformation, the C–H bonds on
adjacent carbon atoms are parallel and lie in the same plane
– In the other extreme, the staggered conformation, the
hydrogen atoms are positioned as far from one another as
possible
Conformational Isomers
• Newman projections are useful for predicting the stability
of conformational isomers
– The eclipsed conformation is higher in energy than the
staggered conformation because of electrostatic repulsions
between hydrogen atoms
– The staggered conformation is the most stable because
electrostatic repulsion between the hydrogen atoms on
adjacent carbons is minimized
Newmans projections
Constitutional (Structural) Isomers
• Constitutional (structural) isomers differ in
the connectivity of the atoms
– The two alcohols, 1–propanol and 2–propanol, have the same
molecular formula (C3H8O), but the position of the –OH group
differs, which causes differences in their physical and
chemical properties
• In the conversion of one constitutional isomer to
another, at least one bond must be broken and
reformed at a different position in the molecule
Propanol…
Stereoisomers
• Stereoisomers are molecules that have the same connectivity but
whose component atoms have different orientations in space
• Two types of stereoisomers:
1. Geometric isomers differ in the relative placement of substituents in a
rigid molecule; members of an isomeric pair are either cis or trans,
with interconversion between the two forms requiring breaking and
reforming one or more bonds; their structural differences causes
them to have different physical and chemical properties and to exist as
two distinct chemical compounds
Stereoisomers
2. Optical isomers are molecules that are mirror
images but cannot be superimposed on one
another in any orientation
a. Optical isomers have identical physical
properties, although their chemical properties
may differ
b. Molecules that are nonsuperimposable mirror
images of each other are said to be chiral; an
achiral object is one that can be superimposed
on its mirror image
Stereoisomers
Stereoisomers
• Most organic molecules that are chiral have at least one
carbon atom that is bonded to four different groups
– This carbon is designated by an asterisk in structural drawings
and is called a chiral center, chiral carbon atom, asymmetric
carbon atom, stereogenic center, or stereocenter
• A molecule and its non-superimposable mirror image are
called enantiomers!
Stereoisomers
Stereoisomers
• Interactions of enantiomers with other chiral
molecules
 In living organisms, every molecule with a stereocenter is found
as a single enantiomer, not a mixture
 At the molecular level, our bodies are chiral and interact
differently with the individual enantiomers of a particular
compound
 Only one enantiomer of a chiral substance interacts with a
particular receptor, initiating a response; the other enantiomer
may not bind at all, or it may bind to another receptor, producing
a different response
Cis and Trans
conformations
Reactivity of Organic Molecules
 The reactivity of a molecule is affected by the degree of
substitution of the carbon bonded to a functional group;
the carbon is designated as primary, secondary, or
tertiary
– Primary carbon is bonded to only one other carbon and a
functional group
– A secondary carbon is bonded to two other carbons and a
functional group
– A tertiary carbon is bonded to three other carbons and a
functional group
Common Classes of
Organic Reactions
 Five common types of organic reactions:
1. Substitution
2. Elimination
3. Addition
4. Free-radical reactions
5. Oxidation-reduction reactions
Substitution
 In a substitution reaction, one atom or group of atoms
in a substance is replaced by another atom or group of
atoms from another substance
 A typical substitution reaction is the reaction of hydroxide
ion with methyl chloride
CH3Cl + OH–  CH3OH + Cl–
 Methyl chloride has a polar C–Cl bond, so the carbon atom has
a partial positive charge
 Electronegative Cl atom is replaced by another electronegative
species that is a stronger nucleophile, OH–
Elimination
 Reactions in which adjacent atoms are removed, or
“eliminated,” from a molecule with the formation of a
multiple bond and a small molecule are called
elimination reactions
 General form:
Addition
 A reaction in which the components of a species A–B
are added to adjacent atoms across a carbon-carbon
multiple bond is called an addition reaction
 An example is the reaction of HCl with ethylene to give
chloroethane:
HCl + CH2CH2  CH3CH2Cl
Free-Radical Reactions
 Many important organic reactions involve free radicals,
and the best known is the reaction of a saturated
hydrocarbon with a halogen:
CH3CH3 + Br2  CH3CH2Br + HBr
• Free radical reactions occur in three stages: initiation,
propagation, and termination
 At high temperature or in the presence of light, the weak Br–Br
bond is broken in an initiation step that produces a number of
Br atoms
 During propagation, a bromine atom attacks ethane, producing
a free radical, which then reacts with another bromine molecule
to produce ethyl bromide; the sum of the propagation steps
corresponds to the overall balanced equation for the reaction
 Three possible termination steps: the combination of two
bromine atoms, of two ethyl radicals, or of an ethyl and a
bromine radical
HALOGEN ELEMENTS
Are a group in the periodic table consisting of
five chemically
related elements, fluorine (F), chlorine(Cl),
bromine (Br), iodine (I), and astatine (At).
In the modern IUPAC nomenclature, this
group is known as group 17 in PSE
Oxidation-Reduction Reactions
 Oxidation-reduction reactions are common in organic
chemistry and can be identified by changes in the
number of oxygens at a particular position in the
hydrocarbon skeleton or in the number of bonds
between carbon and oxygen at that position
General Properties and Reactivity
of Functional Groups
 The functional groups characteristic of each class of
organic compounds determine the general properties
and reactivity of that class
Readings…
 Follow the slides and the book chapter 24
named ORGANIC COMPOUNDS
 http://www.chemguide.co.uk/basicorg/conv
entions/names.html
This link is for additional tutorial for naming
of simple organic compound…
Two more lectures to go…