Transcript Document

Chapter 24
Organic Chemistry
8–1
John A. Schreifels
Chemistry 212
Chapter 24-1
Overview
• Bonding of Carbon
• Hydrocarbons
–
–
–
–
Alkanes and Cycloakanes
Alkenes and Alkynes
Aromatic Hydrocarbons
Naming Hydrocarbons
• Derivatives of Hydrocarbons
– Organic compounds containing Oxygen
– Organic compounds containing Nitrogen
8–2
John A. Schreifels
Chemistry 212
Chapter 24-2
Bonding of Carbon
• Carbon has 4 valence electrons (2s22p2)  needs 4
electrons to fill octet.
– sp3 hydbridization: four bonds to carbon, CH4
– sp2 hydridization: three bonds to carbon; two single bonds
and 1 double bond. CH2=CH2
– sp hybridization: two bonds to carbon; 1 single bond and 1
triple bond, CH≡CH
• Carbon can bond to other carbon atoms to form very
extensive and complicated molecular systems.
8–3
John A. Schreifels
Chemistry 212
Chapter 24-3
Hydrocarbons
• Compounds containing only carbon and hydrogen
– Saturated hydrocarbons contain only single bonds and are
sp3 hybridized. (aliphatic)
– Unsaturated hydrocarbons contain at least one double or
triple bond. (aliphatic)
– Aromatic hydrocarbons: very stable unsaturated compounds
such as benzene: C6H6.
A = propane
B = cyclohexane
C = acetylene
D = benzene
8–4
John A. Schreifels
Chemistry 212
Chapter 24-4
Alkanes and Cycloalkanes
•
•
•
•
Alkanes = acyclic (not cyclic) saturated hydrocarbons
Cycloalkanes = cyclic saturated hydrocarbons.
Molecular formula: gives number and kind of atoms
Structural formula: gives how bonding between different atoms.
H
H C
H
H
structural formula
CH4
molecular formula
8–5
John A. Schreifels
Chemistry 212
Chapter 24-5
Alkanes
• Often called Paraffins
• General formula CnH2n+2 where n = 1 …
E.g. n = 1  CH4; n = 2  C2H6, etc.
• Straight chain (normal) alkanes = carbon atoms connected to each
other to form a chain of carbon atoms:
H
H H
H H H
H H H H
H C H H C C H H C C C H H C C C C H
H
H H
CH4
CH3CH3
Methane
John A. Schreifels
Chemistry 212
Ethane
H H H
CH3CH2CH3
Propane
H H H H
CH3(CH2)2CH3
Butane
8–6
Chapter 24-6
Alkanes: Homologous Series
• Homologous series: series of compounds which differ
by fixed number of atoms (e.g. for alkanes they differ
only by –CH2- group.
• The names and physical properties of the first ten
alkanes are shown on Fig. 24.1
• Physical properties of homologous series vary in a
predictable manner.
– MP and BP increase with number of carbons (Molecular
Mass).
8–7
John A. Schreifels
Chemistry 212
Chapter 24-7
Branched Chain Alkanes; Constitutional
Isomers
• Branched chain alkanes such as isobutane are
hydrocarbons with carbons not always arranged in a
straight chain.
• Butane and Isobutane have the same molecular
formula, but different structure.
• Constitutional (Structural) Isomer – compounds with
the same molecular formula but different structural
formula. Butane and Isobutane (2-methyl propane)
are structural Isomers.
8–8
John A. Schreifels
Chemistry 212
Chapter 24-8
Cycloalkanes
• Hydrocarbons where the carbons form a ring or cyclic
structure; General formula: CnH2n.
8–9
John A. Schreifels
Chemistry 212
Chapter 24-9
Alkenes and Alkynes
• Unsaturated (contains one or more double or triple bonds)
hydrocarbons
• Double and triple bonds are more reactive than single bonds
which makes unsaturated hydrocarbons more reactive than
saturated hydrocarbons.
• Alkenes (CnH2n) are also called olefins and contain carbon –
carbon double bonds.
– All atoms around the double bond are in a plane
– Molecules containing a double bond can have geometric isomer
when there are the same groups on each side of the molecule but
they are located in slightly different positions. E.g. 2 - butene exists
as cis and trans isomers
H
CH3
H
H
C C
C
C
H3C
H
H3C
CH3
8–10
cis-2-butene
John A. Schreifels
Chemistry 212
trans-2-butene
Chapter 24-10
Alkenes: Addition & Oxidation Reactions
• Oxidation: Alkenes can be partially oxidized by permanganate
to produce a brown precipitate called manganese dioxide:
3C2H5CH=CH2 + 2MnO4(aq) + 4H2O  3C2H5CHOHCH2OH +
2MnO2(s) + 2OH (aq)
• Addition: Reactant is added to the two carbons that form the
multiple bond:
H2C=CH2 + Br2  H2CBrCH2Br
– Addition of H2 (called hydrogenation) gives a hydrocarbon
H2C=CH2 + H2  CH3CH3
– Unsymmetrical molecules (e.g. HCl, HBr) can add in two ways:
CH3HC=CH2 + HBr
CH3CH2CH2Br
or
CH3CHBrCH3
Markownikoff’s Rule: addition of unsymmetrical reagent gives
product in which the hydrogen adds to the carbon with the most
hydrogens attached to it => the second product is the dominant
one.
John A. Schreifels
Chemistry 212
8–11
Chapter 24-11
Alkynes
• Alkynes are compounds containing triple bonds.
• Addition reactions of alkynes behave similarly to
alkenes (Markownikoff’s rule):
HC CH + 2HBr
H3C CHBr2
8–12
John A. Schreifels
Chemistry 212
Chapter 24-12
Aromatic Hydrocarbons
• A cyclic compound containing several degrees of
unsaturation (double bonds).
• Aromatic compounds have resonance hybrids and thus are
more stable than normal unsaturated compounds. E.g. Cl2
does not readily add to an aromatic double bond, but reacts
quite rapidly with normal unsaturated compounds.
Benzene
Naphtalene
Anthracene
CH3
8–13
John A. Schreifels
Chemistry 212
Toluene
Chapter 24-13
Reactions on Aromatic Rings: Substitution
• Aromatic Substitution
NO2
H2SO4
reaction – Aromatic
+ H2O
+ HNO3
compound loses a
hydrogen atom and
another atom or group
takes its place.
NO2
NO2
NO2
• It is possible for
NO2
substitution to occur in
NO2
more than one place on
NO2
ortho-Dinitrobenzene para-Dinitrobenzene meta-Dinitrobenzene
the ring.
8–14
John A. Schreifels
Chemistry 212
Chapter 24-14
Naming Alkanes
• Straight-Chain Alkanes (see Table
24.1)
• Branched chain has substituents on
the molecule; does not form a single
simple straight chain.
• Name branched-chain alkanes using
the format: Prefix-Parent-Suffix
– Prefix specifies position and number of
various substituents
– Parent tells how many carbons atoms are
present on the longest continuous chain.
– Suffix tells to what family the molecule
belongs (alkanes: -ane; alkenes: -ene,
etc)
John A. Schreifels
Chemistry 212
CH3CH2CHCH3
CH3
Branched Chain Alkane
8–15
Chapter 24-15
Naming Alkanes
• Determine the longest chain; use the name of that chain as
the parent name; be careful to look for the longest chain.
– The name of the chain below would be hexane not butane.
CH3CH2CHCH3
CH2CH2CH3
3-methylhexane
• Number carbons starting from end nearest substituent.
• Name and locate each substituent group (-ane becomes –yl
ending)
• With two or more substituents list them in alphabetical order;
use di-, tri- etc. for identical substituents.
H3C H3C
CH
H3C
C
CH2CH3
CH2CH3
8–16
3-ethyl-2,3dimethylpentane
John A. Schreifels
Chemistry 212
Chapter 24-16
Functional Groups
• Organic compounds often contain elements other
than C, H that increase their reactivity.
• Functional Groups are the reactive portions of the
molecule that undergo predictable reactions
depending upon the functional group.
8–17
John A. Schreifels
Chemistry 212
Chapter 24-17
List of Organic Functional Groups
8–18
John A. Schreifels
Chemistry 212
Chapter 24-18
Names and Properties of the Straight Chain Alkanes
8–19
Return to Slide 7
John A. Schreifels
Chemistry 212
Return to Slide 15
Chapter 24-19