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Spring 2014
Lecture 10:Organic Compounds
Course lecturer : Jasmin Šutković29 th April 2014
Contents International University of Sarajevo
1. Functional classes and types of Org. CompoundsAlkanesAlkenesAlkynesAromatic compounds
2. Isomeric variations of Organic compounds
3. Reactivity of Organic compound
4. Chemical reactions of Organic Compounds SubstitutionAdditionElimination
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
CnH2n+2 CH4
C2H6
C3H8
C4H10
etc.
C2H6 ethane H H
H—C—C—H H HSingle bond…
ALKANES
• sp3 conformation
• bond angles = 109.5o
• σ-bonds (sigma)
Rotation about C--C (conformations)
CH
HH
HCHH
C3H8 propane
H C C C HH
H
H
H
H
H
projection formula
CH3CH2CH3 partially condensed formula
C4H10 butane(s)
H C C C CH
H
H
H
H
HH
H
HH C C C
H
H
C
H
HH
H
HH
H
CH3CH2CH2CH3 CH3CHCH3
CH3
projection
partially condensed
stick formulas
Two isomers of butane C4H10:
CH3CH2CH2CH3 n-butane
CH3CH3CHCH3 isobutane
Isomers are different compounds that have the same molecular formula
Alkane nameCH4 methane C2H6 ethaneC3H8 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
CH3CH3CH2CH2CH2CH2CH3 CH3CHCH2CH2CH3 n-hexane 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” |
CH3CH2CH2Br BrCH2CH2CH3 CH3CH2CH2Br
n-propyl bromide
CH3CHCH3Br
CH3CHBrCH3 CH3
CHBrCH3
isopropyl bromide
CH3CH2CH2CH2Cl CH3CH2CH2CH2Cl
ClCH2CH2CH2CH3
n-butyl chloride
CH3CHCH2CH3Cl
CH3CH2CHCH3Cl
CH3CH2CHCH3
Cl
sec-butyl chloride
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 gaspetroleumcoal
petroleum is a complex mixture of hydrocarbons1. solvents2. fuels3. raw materials for chemical syntheses
separated into fractions by fractional distillation in an oil refinery
Alkenes CnH2n
“unsaturated” hydrocarbons
C2H4 ethylene
Functional group = carbon-carbon double bond
sp2 hybridization => flat, 120o bond angles
σ bond & π bond => H2C=CH2
C CH
H H
H
C3H6 propylene CH3CH=CH2
C4H8 butylenes CH3CH2CH=CH2
α-butylene 1-butene
CH3CH3CH=CHCH3 CH3C=CH2
β-butylene isobutylene 2-butene 2-methylpropene
There are two 2-butenes:
cis-2-butene trans-2-butene
“geometric isomers” (diastereomers)
C C C CH3C
H H
CH3 H3C
H CH3
H
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” (E)- “entgegen”
together opposite
CIS /TRANS or E-Z systems
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.
C CH
H3C CH2CH3
CH3
C CH3C
H Br
Cl
*
* *
*
(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 CH3CCH 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.
CH3CH2CCCH3 2-pentyne
ethylmethylacetylene
“terminal” alkynes have the triple bond at the end of the chain:
CH3CH3CH2CCH HCCCHCH2CH3
1-butyne 3-methyl-1-pentyne ethylacetylene 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
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
Organic compounds groups :
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 (> CO), 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
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
Reactivity of Organic Molecules
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 + CH2CH2 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/conventions/names.html
This link is for additional tutorial for naming of simple organic compound…
Two more lectures to go…