Chapter 2: Alkanes Alkanes from Carbon and Hydrogen

Home , Cycloheptane, Ethane, Isopropyl chloride, Isopropyl iodide, Nonane

•Alkanes are carbon compounds that contain only single bonds. •The simplest alkanes are hydrocarbons – compounds that contain only carbon and hydrogen. •Hydrocarbons are used mainly as fuels, solvents and lubricants:

H H H H H H H H H H H H C H C C H C C C C H H C C C C C H H H C C H H H H H H CH2 H CH3 H H H H CH3

# of carbons boiling point range Use

1-4 <20 °C fuel (gasses such as methane, propane, butane)

5-6 30-60 solvents (petroleum ether)

6-7 60-90 solvents (ligroin)

6-12 85-200 fuel (gasoline)

12-15 200-300 fuel (kerosene)

15-18 300-400 fuel (heating oil)

16-24 >400 lubricating oil, asphalt Hydrocarbons

Formula Prefix Suffix Name Structure H

CH4 meth- -ane methane H C H H C H eth- -ane ethane 2 6 H3C CH3

C3H8 prop- -ane propane

C4H10 but- -ane butane

C5H12 pent- -ane pentane

C6H14 hex- -ane hexane

C7H16 hept- -ane heptane

C8H18 oct- -ane octane

C9H20 non- -ane nonane

C10H22 dec- -ane decane Hydrocarbons

Formula Prefix Suffix Name Structure

CH4 meth- -ane methane H C H

H H

C2H6 eth- -ane ethane H C C H

H H

H C H prop- -ane propane 3 8 H3C C CH3 or H

H H C H 4 10 but- -ane butane H3C C C CH3 or H H

H C H 4 10 but- -ane butane? H3C C CH3 or

CH3 HydHrydorcocaarrbobnos ns

Formula Prefix Suffix Name Structure

CH4 meth- -ane methane H C H

H H

C2H6 eth- -ane ethane H C C H

H H

C3H8 prop- -ane propane H3C C CH3 or H

H H C H 4 10 but- -ane butane H3C C C CH3 or H H

H C H 4 10 but- -ane iso-butane H3C C CH3 or

CH3 HydHrydoroccarbrobnsons

Formula Prefix Suffix Name Structure

H H C H 4 10 but- -ane butane H3C C C CH3 or H H

H C H but- -ane iso-butane 4 10 H3C C CH3 or

CH3

H H H C H pent- -ane pentane 5 12 H3C C C C CH3 or H H H

H H H

C5H12 pent- -ane iso-pentane H3C C C C H or

H CH3 H

H CH3 H or C5H12 pent- -ane iso-pentane???H C C C H

H CH3 H HydHrydoroccarbrobnsons

Formula Prefix Suffix Name Structure

H H C H 4 10 but- -ane butane H3C C C CH3 or H H

H C H but- -ane iso-butane 4 10 H3C C CH3 or

CH3

H H H C H pent- -ane pentane 5 12 H3C C C C CH3 or H H H

H H H

C5H12 pent- -ane iso-pentane H3C C C C H or

H CH3 H

H CH3 H or C5H12 pent- -ane neo-pentane H C C C H

H CH3 H IUPAC System of Naming Organic Compounds

1. Find the longest carbon chain

2. Name all the atoms (other than H) not in the longest chain as groups

3. Number groups from the end of the chain closest to the first group

4. List multiple groups in alphabetical order,

H H H IUPAC Name 2 4 Longest chain: pentane H3C C C C CH3 pentane 1 3 5 Groups: none H H H

H H H 3 1 4 2 Longest chain: butane 2-methylbutane H3C C C C H Groups: one methyl not: 3-methylbutane H CH H 3 not: 2 4 1 3

3 H CH3 H Longest chain: propane 2 2,2-dimethylpropane H C C C H 1 Groups: two methyls

H CH3 H IUPAC System of NHyadrmocianrbgon sOrganic Compounds

Formula Prefix Suffix IUPAC Name Structure

H H C H -ane 4 10 but- butane H3C C C CH3or H H

C4H10 but- -ane iso-butane H3C C CH3

CH3

H H H C H pent- -ane pentane 5 12 H3C C C C CH3 H H H

H H H C H pent- -ane 5 12 2-methyl butane H3C C C C H

H CH3 H

C5H12 pent- -ane 2,2-dimethylpropane H C C C H

H CH3 H Naming Branches as “Groups” Naming Branches as Groups

Group Formula Prefix Suffix Name Abbreviation Structure

–CH3 meth- -yl methyl –Me C H

H H H

C C H –C2H5 eth- -yl ethyl –Et H H

H H

C C CH3 or –C3H7 prop- -yl propyl –Pr H H

H3C C CH3 or –C3H7 iso-prop- -yl iso-propyl –iPr

H H H

–C4H9 but- -yl butyl –Bu C C C CH3 or H H H Naming Branches as “Groups” Other Groups We May Encounter

Group Formula Name Structure Group Formula Name Structure

–C4H9 iso-butyl –F fluoro –F

–C4H9 sec-butyl –Cl chloro –Cl

–Br bromo –Br –C4H9 tert-butyl

–I iodo –I –C5H11 neo-pentyl Structural Isomers How many structural isomers – compounds with the same chemical formula but different connectivity – are there with the formula C7H16? Structural Isomers How many structural isomers – compounds with the same chemical formula but different connectivity – are there with the formula C7H16?

IUPAC Name IUPAC Name CH3 2 4 6 2 4 heptane 2,2-dimethylpentane 1 3 5 7 1 3 5 CH3

CH3 CH3 4 6 3 2 2-methylhexane 2 4 2,3-dimethylpentane 1 3 5 1 5 CH3

2 4 6 CH3 CH3 3 3-methylhexane 1 5 2 4 2,4-dimethylpentane 1 3 5 CH3

CH3 2 CH34 2 6 3,3-dimethylpentane 4 4-methylhexane 1 3 5 1 3 5 CH3

2 4 CH3 3 – –2 3 6 1 5 3-ethylpentane 3-methylhexane 6 5 4 –4 2 1 –1 3– 5– 1 CH3 2 3-methylhexane 3 –4 2 4 4 6 H C –2 5 2-ethylpentane 2,2,3-Trimethyl-butane 3 –3 5– 1 3 1– Methyl and Ethyl Compounds Methyl & Ethyl Compounds

Group Formula Name Abbreviation Structure H

H3C– methyl –Me C H

H H H

H5C2– ethyl –Et C C H

H H

methane H3C–H H5C2–H ethane methyl alcohol (methanol) H3C–OH H5C2–OH ethyl alcohol (ethanol)

H C–NH methylamine (aminomethane) 3 2 H5C2–NH2 ethylamine (aminoethane) methyl fluoride (fluoromethane) H3C–F H5C2–F ethyl fluoride (fluoroethane) methyl chloride (chloromethane) H3C–Cl H5C2–Cl ethyl chloride (chloroethane)

H C–Br methyl bromide (bromomethane) 3 H5C2–Br ethyl bromide (bromoethane) methyl iodide (iodomethane) H3C–I H5C2–I ethyl iodide (iodoethane) methyl cyanide (cyanomethane, acetonitile) H3C–CN H5C2–CN ethyl cyanide (cyanoethane, proprionitile)

H C–SH methanethiol (methyl mercaptan) 3 H5C2–SH ethanethiol (ethyl mercaptan) Methyl and Ethyl Compounds Methyl & Ethyl Compounds

Group Formula Name Abbreviation Structure H

H3C– methyl –Me C H

H H H

H5C2– ethyl –Et C C H

H H

H H C H C H H C–H methane H C H5C2–H ethane H 3 3

H3C methyl cation H3C–CH2 ethyl cation

C C H H H H H C methyl radical H C H3C–CH2 ethyl radical H 3 3

H3C methyl anion H3C–CH2 ethyl anion C C H H H H H C H 3 Propyl Compounds Propyl Compounds

Group Formula Name Abbreviation Structure H H or H7C3– prop- –Pr C C CH3 H H H H7C3– i iso-prop- – Pr H3C C CH3 or

3 1 HO 2 3 OH propyl alcohol (1-propanol) 2 isopropyl alcohol (isopropanol; 2-propanol)

H2N 1 propyl amine (1-aminopropane) NH2 isopropyl amine (2-aminopropane) F F propyl fluoride (1-fluoropropane) isopropyl fluoride (2-fluoropropane) Cl Cl propyl chloride (1-chloropropane) isopropyl chloride (2-chloropropane) Br Br propyl bromide (1-bromopropane) isopropyl bromide (2-bromopropane) I I propyl iodide (1-iodopropane) isopropyl iodide (2-iodopropane) Structural Isomers of C7H16

2 4 6 7 heptane What if we attatch the two ends together? 1 3 5

1 H2 7 2 C H2C CH2 6 3 H2C CH2 5 4 H2C CH2

cycloheptane C7H14

Cycloheptane contains two fewer hydrogens than heptane. They are not structural isomers. CyCcyclloaalklakneas nes

Compound Name Structure Group Name Structure

cyclopropane cyclopropyl

cyclobutane cyclobutyl

cyclopentane cyclopentyl

cyclohexane cyclohexyl

cycloheptane cycloheptyl

cyclooctane cyclooctyl Naming Cycloalkanes

Unlike "floppy" chains, rings have an additional consideration for multiple substitutions:

Me Me Me Me H H H

H H H Me Me H H

"flat" 1,2-dimethylcyclopropane "3-D" 1,2-dimethylcyclopropane "3-D" 1,2-dimethylcyclopropane

These are different compounds! They cannot be interconvertied by bond rotation.

Me Me Me H H H

H H H Me H H

cis-1,2-dimethylcyclopropane trans-1,2-dimethylcyclopropane

cis – substituents on same side (of the ring) trans – substituents on opposite sides (of the ring)

The above compounds are not structural isomers. Their connectivity is identical. They are stereoisomers – compounds that differ in how substituents are arranged in space Naming Cycloalkanes IUPAC Naming of Rings

How can we represent cis/trans isomers in a flat drawing?

Me Me Me Me Me H H H

H H H Me H H Me Me cis-1,2-dimethylcyclopropane trans-1,2-dimethylcyclopropane

A solid wedge means the bond is A dashed wedge means that the bond pointing "up" and out of the page is pointing "down" and into the page NaIUmPAinC gN amCinygc ofl oRianglskanes

Don't let the wedges and dashes confuse you:

Me Me

cis-1,2-dimethylcyclopropane cis-1,2-dimethylcyclopropane

These are the same compound!

Me Me H

H H Me H Flip over 180°

Me H H H

Me Me H

Me 3-Dimensional Structure/VSEPR Theory

A dashed wedge means: the substituent X is behind the plane of the paper

109° X Atoms place substituents as far appart as possible: A X X X A X A solid wedge means: the substituent is X in front of the plane of the paper A = any atom X X = any substituent (atom or lone pair)

H H F

C N O B H H F H H H F H H F

tetrahedral electron-domain geometries 3-Dimensional Structure

H H H H H H C C H C C H H H H H each carbon is tetrahedral "flat" ethane wedge/dash depiction of ethane

H H H

C C

H H H

"3-D" ethane 3-Dimensional Structure The Conformation of Ethane

If we look down the C–C bond axis, we get a different perspective:

H H H H H H C C C H H H H H H

We can use a Newman Projection to depict this view: The large circle is a stylized representation of the back atom

H H

Front atom appears at vertex here

H H H Newman Projection

But there is free rotation around single (!) bonds:

these hydrogens are in H the same plane H H H H H H H H H C C C C H H H H H H H H H H H H H H these hydrogens are in The "staggered" conformation the same plane The "eclipsed" conformation 3-Dimensional Structure

these hydrogens are H in the same plane H H H H H H H H H C C C C H H H H H H H H H H H H H H these hydrogens are The "staggered" conformation in the same plane The "eclipsed" conformation

The staggered conformation is the lowest energy conformation The elclpsed conformation is the highest energy confornation

H H H H H

H H H H H H H

The energy minimum The energy maximum

Molecules that differ by only rotations around single bonds are conformational Isomers. 3-Dimensional Structure

Place substituents as far appart as possible:

180°

H3CCN H3C C N Molecule is linear

120° B BF3 F F Molecule is trigonal planar

2s 2px 2py 2pz H

109° 2nd row valence orbitals

CH4 C H H H Molecule is tetrahedral

How can these molecular shapes arise from bonding between the available orbitals? Hybridization

180°

H3CCN H3C C N Molecule is linear

2s 2px 2py 2pz

2nd row valence orbitals

this side gets bigger and 50% more spherical this side gets smaller and 50% more spherical

mixing 2px C C and C

2 unhybridized orbitals 2 sp-hybridized orbitals Only "X"-directionality; 50% s-like and 50% p-like

H C C N H3C C N 3 H3C C N

sp-orbitals on the central carbon atom the !-bond formed by sp-orbital overlap

"-bonding in the triple bond Hybridization

120° BF 3 B

F F Molecule is trigonal planar 2s 2px 2py 2pz

2nd row valence orbitals

this side gets bigger and 33% more spherical this side gets smaller and 33% more spherical

C mixing and and 2px C C C 2s

2py

3 sp-hybridized orbitals 3 unhybridized orbitals Only "X" and "Y"-directionality; 33% s-like and 67% p-like

F F

B F B F

F F

All 3 sp2-orbitals on the boron atom The !-bonds between boron and fluorine Hybridization

109°

CH4 C H H H 2s 2px 2py 2pz Molecule is tetrahedral

2nd row valence orbitals

H H

mixing C C H H H H H H 2s 2px 2py 2pz All 4 sp3-orbitals on the carbon atom The !-bonds between carbon and hydrogen

All 4 unhybridized orbitals Each orbital has "X", "Y" and "Z"-directionality and are 25% s-like and 75% p-like