8–1 John A. Schreifels Chemistry 212 Chapter 24-1 Chapter 24 Organic Chemistry

John A. SchreifelsChemistry 212

Chapter 24-1

8–1

Chapter 24

Organic Chemistry


Chapter 24-2

8–2

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


Chapter 24-3

8–3

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.


Chapter 24-4

8–4

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 = propaneB = cyclohexaneC = acetyleneD = benzene


Chapter 24-5

8–5

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.

C

H

H

H

H

structural formula

CH4

molecular formula


Chapter 24-6

8–6

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:

C

H

H

H

H C

H

H

H

C

H

H

H C

H

H

H

C

H

H

C

H

H

H C

H

H

H

C

H

H

C

H

H

C

H

H

H

CH4 CH3CH3 CH3CH2CH3 CH3(CH2)2CH3

Methane Ethane Propane Butane


Chapter 24-7

8–7

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).


Chapter 24-8

8–8

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.


Chapter 24-9

8–9

Cycloalkanes

• Hydrocarbons where the carbons form a ring or cyclic structure; General formula: CnH2n.


Chapter 24-10

8–10

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

CH3CC

H3C

HH CH3CC

H3C H

H

cis-2-butene trans-2-butene


Chapter 24-11

8–11

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:

CH3CHBrCH3

CH3HC=CH2 + HBror

CH3CH2CH2Br

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.


Chapter 24-12

8–12

Alkynes

• Alkynes are compounds containing triple bonds.• Addition reactions of alkynes behave similarly to

alkenes (Markownikoff’s rule):

HC CH 2HBr H3C CHBr2+


Chapter 24-13

8–13

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.

CH3

Benzene Naphtalene Anthracene

Toluene


Chapter 24-14

8–14

Reactions on Aromatic Rings: Substitution

• Aromatic Substitution reaction – Aromatic compound loses a hydrogen atom and another atom or group takes its place.

• It is possible for substitution to occur in more than one place on the ring.

H2SO4

NO2

+ HNO3 + H2O

NO2

NO2

NO2

NO2

NO2

NO2

ortho-Dinitrobenzene para-Dinitrobenzene meta-Dinitrobenzene


Chapter 24-15

8–15

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)

CH3CH2CHCH3CH3

Branched Chain Alkane


Chapter 24-16

8–16

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.

• 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.

CH3CH2CHCH3CH2CH2CH3

3-methylhexane

H3C

CH

H3C

C

H3C

CH2CH3

CH2CH3

3-ethyl-2,3dimethylpentane


Chapter 24-17

8–17

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.


Chapter 24-18

8–18

List of Organic Functional Groups


Chapter 24-19

8–19

Names and Properties of the Straight Chain Alkanes

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8–1 John A. Schreifels Chemistry 212 Chapter 24-1 Chapter 24 Organic Chemistry