Organic Chemistry Chapter 3

organic chemistry

the chemistry of carbon
on planet earth, all accessible carbon is processed through living organisms

carbon cycle

all available planetary carbon is processed as "organic" carbon over and over

other important elements in organic chemistry

Li,Na, K, Mg, N, Ca, P, O, S, Cl, Br, I

what's the big deal about carbon chemistry?

-there are <16 million known organic compounds(majority of compounds)
-there are in theory an infinite number of organic compounds
-new organic compounds of desired structure are created every day by:
-chemisits/biochemists
-organisms

why is carbon chemistry pervasive?

-carbon forms covalent bonds with itself using single, double, and triple bonds
-carbon forms covalent and/or ionic bonds with >90 elements (no noble gases or highly radioactive elements)

hydrocarbons

compounds containing only Carbon and Hydrogen

universal alkane formula

CnH(2n+2)
n=number of carbons
2n+2=number of hydrogens

rule of four

in stable organic molecules, all carbons have four bonds
Carbon attached to 4 atoms is always sp3 hybridized-tetrahedral geometry

constitutional isomerism

molecules that have the same formula, but different atom-atom connection
different compounds therefore have different physical properties

Naming an alkene

1.) identify the longest chain of carbons
2.) number the chain from 1,2...n such that carbon 1 is assigned to the beginning of the chain and the first branch is minimized
3.) name the alkyl groups and assign their locations using your numbering system

Isobutane

2-methylpropane=IUPAC

Acetylene

Ethyne=IUPAC

1* primary carbon

Carbon attached to one other carbon

2* secondary carbon

Carbon attached to 2 other carbons

3* tertiary carbon

Carbon attached to 3 other carbons

4* quaternary carbon

Carbon attached to 4 other carbons

1* primary hydrogen

Hydrogen attached to 1* carbon

2* secondary hydrogen

Hydrogen attached to 2* carbon

3* tertiary hydrogen

Hydrogen attached to 3* carbon

General cycloalkane formula

CnH2n

Conformations of alkanes

Conformations are structures that interconvert by rotation about carbon-carbon single bonds
Any 3-D arrangement of atoms in a molecule that results by rotation about a single bond
Equivalent term: "conformational isomers"
Carbon-carbon single bonds tend t

Staggered conformation

a conformation about a carbon to carbon single bond in which the atoms on one carbon are as far apart as possible from the adjacent carbon
More stable than eclipsed conformation

Torsion strain

Inherent instability caused by eclipsing
arises when atoms separated by 3 bonds are forced from a staggered conformation to an eclipsed conformation

Cis-trans isomers

isomers that have the same order of attachment of their atoms, but a different arrangement of their atoms in space, due to the presence of either a ring or a carbon-carbon double bond
Cis-trans isomers do not interconnect
They are not constitutional isome

Cis isomers

Have 2 substituents on the same side of the plane

Trans isomers

Have 2 substituents on the opposite sides of the plane

Axial bonds

bond on a chair conformation of a cyclohexane ring that extends from ring parallel to imaginary axis of ring
Straight up and down
3 bonds point up, other three point down
if axial bond on carbon points upward, equatorial bond on that carbon points slightl

Equatorial bonds

bond on chair conformation of cyclohexane ring that extends from the ring roughly perpendicular to the imaginary axis of ring
Directed outward
alternate:1st slightly up and then slightly down
Substituents larger than H prefer to be equatorial
Bigger subst

Physical properties of alkanes

-nonpolar
-soluble in most organic solvents, insoluble in water
-boiling points increase with increasing molecular weight
-when comparing constitutional isomers, the boiling point decreases with greater chain branching--more branched structures=boils at a

Role of dispersion forces for liquid alkanes

Alignment of induced dipoles causes adjacent molecules to stick together
Round or branched alkanes do not align efficiently so they stick together less...smaller area of contact. Therefore lower boiling point

Combustion reaction of an alkane

CnH(2n+2)+((3n+1)/2)O2 --> nCO2+(n+1)H2O
All C become CO2
All H become H2O

Line angle formula

Each line ending represents a carbon atom and a line represents a bond
A carbon at every bend and at every end

Alkyl group

Group derived by removing a hydrogen from an alkane
Given the symbol -R

Iso

For names beyond propane, iso indicates the one end of an otherwise unbranched chain terminates in a (CH3)2CH group

Cycloalkane

Saturated hydrocarbon that contains carbon atoms joined to form a ring
Contains two fewer hydrogen atoms than an alkane with the same number of carbon atoms

IUPAC system of nomenclature

1. Prefix: number carbon atoms in parent chain
2. Infix: nature of C-C bonds in parent chain
-an: all single bonds
-en: one or more double bonds
-yn: one or more triple bonds
3. Suffix: class of compound to which substance belongs
-e: hydrocarbon
-ol: alc

eclipsed conformation

a conformation about a C-C single bond in which the atoms on one carbon are as close as possible to the atoms on the adjacent carbon

angle strain

strain that arises when a bond angle is either compressed or expanded compared with its optimal value

chair conformation

most stable puckered conformation of a cyclohexane ring; all bond angles are about 109.5* and bonds to all adjacent carbons are staggered
-99.9% of all cyclohexanes are in the chair conformation

boat conformation

a puckered conformation of a cyclohexane ring in which carbons 1 and 4 of the ring are bent toward each other
-less stable than chair conformation
-torsional strain is created by 4 sets of eclipsed hydrogen interactions and steric strain created by one se

steric strain

strain that arises when atoms separated by 4 or more bonds are forced abnormally close to one another(forced closer than their atomic radii allow)

chemical property of alkanes and cycloalkanes

interness
quite unreactive toward most reagents(nonpolar and only sigma bonds)
will react with O2(combustion)

major sources of alkanes

fossil fuels (natural gas, petroleum, coal)

organic chemistry

the chemistry of carbon
on planet earth, all accessible carbon is processed through living organisms

carbon cycle

all available planetary carbon is processed as "organic" carbon over and over

other important elements in organic chemistry

Li,Na, K, Mg, N, Ca, P, O, S, Cl, Br, I

what's the big deal about carbon chemistry?

-there are <16 million known organic compounds(majority of compounds)
-there are in theory an infinite number of organic compounds
-new organic compounds of desired structure are created every day by:
-chemisits/biochemists
-organisms

why is carbon chemistry pervasive?

-carbon forms covalent bonds with itself using single, double, and triple bonds
-carbon forms covalent and/or ionic bonds with >90 elements (no noble gases or highly radioactive elements)

hydrocarbons

compounds containing only Carbon and Hydrogen

universal alkane formula

CnH(2n+2)
n=number of carbons
2n+2=number of hydrogens

rule of four

in stable organic molecules, all carbons have four bonds
Carbon attached to 4 atoms is always sp3 hybridized-tetrahedral geometry

constitutional isomerism

molecules that have the same formula, but different atom-atom connection
different compounds therefore have different physical properties

Naming an alkene

1.) identify the longest chain of carbons
2.) number the chain from 1,2...n such that carbon 1 is assigned to the beginning of the chain and the first branch is minimized
3.) name the alkyl groups and assign their locations using your numbering system

Isobutane

2-methylpropane=IUPAC

Acetylene

Ethyne=IUPAC

1* primary carbon

Carbon attached to one other carbon

2* secondary carbon

Carbon attached to 2 other carbons

3* tertiary carbon

Carbon attached to 3 other carbons

4* quaternary carbon

Carbon attached to 4 other carbons

1* primary hydrogen

Hydrogen attached to 1* carbon

2* secondary hydrogen

Hydrogen attached to 2* carbon

3* tertiary hydrogen

Hydrogen attached to 3* carbon

General cycloalkane formula

CnH2n

Conformations of alkanes

Conformations are structures that interconvert by rotation about carbon-carbon single bonds
Any 3-D arrangement of atoms in a molecule that results by rotation about a single bond
Equivalent term: "conformational isomers"
Carbon-carbon single bonds tend t

Staggered conformation

a conformation about a carbon to carbon single bond in which the atoms on one carbon are as far apart as possible from the adjacent carbon
More stable than eclipsed conformation

Torsion strain

Inherent instability caused by eclipsing
arises when atoms separated by 3 bonds are forced from a staggered conformation to an eclipsed conformation

Cis-trans isomers

isomers that have the same order of attachment of their atoms, but a different arrangement of their atoms in space, due to the presence of either a ring or a carbon-carbon double bond
Cis-trans isomers do not interconnect
They are not constitutional isome

Cis isomers

Have 2 substituents on the same side of the plane

Trans isomers

Have 2 substituents on the opposite sides of the plane

Axial bonds

bond on a chair conformation of a cyclohexane ring that extends from ring parallel to imaginary axis of ring
Straight up and down
3 bonds point up, other three point down
if axial bond on carbon points upward, equatorial bond on that carbon points slightl

Equatorial bonds

bond on chair conformation of cyclohexane ring that extends from the ring roughly perpendicular to the imaginary axis of ring
Directed outward
alternate:1st slightly up and then slightly down
Substituents larger than H prefer to be equatorial
Bigger subst

Physical properties of alkanes

-nonpolar
-soluble in most organic solvents, insoluble in water
-boiling points increase with increasing molecular weight
-when comparing constitutional isomers, the boiling point decreases with greater chain branching--more branched structures=boils at a

Role of dispersion forces for liquid alkanes

Alignment of induced dipoles causes adjacent molecules to stick together
Round or branched alkanes do not align efficiently so they stick together less...smaller area of contact. Therefore lower boiling point

Combustion reaction of an alkane

CnH(2n+2)+((3n+1)/2)O2 --> nCO2+(n+1)H2O
All C become CO2
All H become H2O

Line angle formula

Each line ending represents a carbon atom and a line represents a bond
A carbon at every bend and at every end

Alkyl group

Group derived by removing a hydrogen from an alkane
Given the symbol -R

Iso

For names beyond propane, iso indicates the one end of an otherwise unbranched chain terminates in a (CH3)2CH group

Cycloalkane

Saturated hydrocarbon that contains carbon atoms joined to form a ring
Contains two fewer hydrogen atoms than an alkane with the same number of carbon atoms

IUPAC system of nomenclature

1. Prefix: number carbon atoms in parent chain
2. Infix: nature of C-C bonds in parent chain
-an: all single bonds
-en: one or more double bonds
-yn: one or more triple bonds
3. Suffix: class of compound to which substance belongs
-e: hydrocarbon
-ol: alc

eclipsed conformation

a conformation about a C-C single bond in which the atoms on one carbon are as close as possible to the atoms on the adjacent carbon

angle strain

strain that arises when a bond angle is either compressed or expanded compared with its optimal value

chair conformation

most stable puckered conformation of a cyclohexane ring; all bond angles are about 109.5* and bonds to all adjacent carbons are staggered
-99.9% of all cyclohexanes are in the chair conformation

boat conformation

a puckered conformation of a cyclohexane ring in which carbons 1 and 4 of the ring are bent toward each other
-less stable than chair conformation
-torsional strain is created by 4 sets of eclipsed hydrogen interactions and steric strain created by one se

steric strain

strain that arises when atoms separated by 4 or more bonds are forced abnormally close to one another(forced closer than their atomic radii allow)

chemical property of alkanes and cycloalkanes

interness
quite unreactive toward most reagents(nonpolar and only sigma bonds)
will react with O2(combustion)

major sources of alkanes

fossil fuels (natural gas, petroleum, coal)