CHEM 212 - Alkanes Review

Introductory Organic Chemistry Chem 212 & Chem 211

Dr. Laura PavelkaDepartment of Chemistry

Pulp & Paper [email protected]

ORGANIC BITES 2A: BASIC ALKANES

CHEM 212/211 Organic Bites 2A ‐ Chapter 4 2

LET’S REVIEW ALKANE NOMENCLATURE...

Section 2 – Alkanes and CycloalkanesChapter 4 – Nomenclature and Conformations

Simple Alkanes and CycloalkanesNaming Branched AlkanesNaming Branched Cycloalkanes

Overview of Alkanes and Cycloalkanes


CYCLOALKANES: rings, all σ‐bonds, tetrahedral, sp3

H

H

H

H

H

H

H

H

H H

H

H

H

HH H

ALKANES: “saturated”, all σ bonds, tetrahedral, sp3

H

CH H

H


Alkanes: “saturated”, only σ‐bonds (CnH2n+2)

CH4 METHANE bp = ‐164 °CCH3CH3 ETHANE C2H6 bp = ‐ 89 °CCH3CH2CH3 PROPANE C3H8 bp = ‐ 42 °C

CC

CH H

HHHH

HH

≡



CH4 METHANE bp = ‐164 °CCH3CH3 ETHANE C2H6 bp = ‐ 89 °CCH3CH2CH3 PROPANE C3H8 bp = ‐ 42 °CCH3CH2CH2CH3 BUTANE C4H10 bp = 0 °C

≡



CH4 METHANE bp = ‐164 °CCH3CH3 ETHANE C2H6 bp = ‐ 89 °CCH3CH2CH3 PROPANE C3H8 bp = ‐ 42 °CCH3CH2CH2CH3 BUTANE C4H10 bp = 0 °CCH3CH(CH3)2 ISOBUTANE bp = ‐11 °C

≡

≡STRUCTURAL ISOMERS(same formula, different connectivity)



CH4 METHANE bp = ‐164 °CCH3CH3 ETHANE C2H6 bp = ‐ 89 °CCH3CH2CH3 PROPANE C3H8 bp = ‐ 42 °CCH3CH2CH2CH3 BUTANE C4H10 bp = 0 °CCH3(CH2)3CH3 PENTANE C5H12 bp = 36 °CCH3CH2CH(CH3)2 ISOPENTANE bp = 28 °CCH3C(CH3)3 NEOPENTANE bp = 10 °C

CC

CH C

HHHH

HH

C

HH

H

HH

≡STRUCTURAL ISOMERS



CH4 METHANE bp = ‐164 °CCH3CH3 ETHANE C2H6 bp = ‐ 89 °CCH3CH2CH3 PROPANE C3H8 bp = ‐ 42 °CCH3CH2CH2CH3 BUTANE C4H10 bp = 0 °CCH3(CH2)3CH3 PENTANE C5H12 bp = 36 °CCH3(CH2)4CH3 HEXANE C6H14 bp = 69 °CCH3(CH2)2CH(CH3)2 ISOHEXANE bp = 60 °CCH3CH2C(CH3)3 NEOHEXANE bp = 50 °CCH3CH2CH(CH3)CH2CH3 bp = 63 °C(CH3)2CHCH(CH3)2 bp = 58 °C

STRUCTURAL ISOMERS



CH4 METHANE bp = ‐164 °CCH3CH3 ETHANE C2H6 bp = ‐ 89 °CCH3CH2CH3 PROPANE C3H8 bp = ‐ 42 °CCH3CH2CH2CH3 BUTANE C4H10 bp = 0 °CCH3(CH2)3CH3 PENTANE C5H12 bp = 36 °CCH3(CH2)4CH3 HEXANE C6H14 bp = 69 °CCH3(CH2)5CH3 HEPTANE C7H16 bp = 98 °CCH3(CH2)6CH3 OCTANE C8H18 bp = 125 °CCH3(CH2)7CH3 NONANE C9H20 bp = 151 °CCH3(CH2)18CH3 EICOSANE C20H42 bp = 343 °C

366 319 structural isomers!



GASES

LIQUIDS

CH4 METHANE bp = ‐164 °CCH3CH3 ETHANE C2H6 bp = ‐ 89 °CCH3CH2CH3 PROPANE C3H8 bp = ‐ 42 °CCH3CH2CH2CH3 BUTANE C4H10 bp = 0 °CCH3(CH2)3CH3 PENTANE C5H12 bp = 36 °CCH3(CH2)4CH3 HEXANE C6H14 bp = 69 °CCH3(CH2)5CH3 HEPTANE C7H16 bp = 98 °CCH3(CH2)6CH3 OCTANE C8H18 bp = 125 °CCH3(CH2)7CH3 NONANE C9H20 bp = 151 °CCH3(CH2)18CH3 EICOSANE C20H42 bp = 343 °C

Cycloalkanes: rings, only σ‐bonds (CnH2n)


ALKANES = CnH2n+2 CYCLOALKANES = CnH2n

DIFFERENCE IN # HYDROGENS = (2n+2) ‐ 2n = 2UNITS OF UNSATURATION = 1 (1 per 2 Hs)

Cycloalkanes: rings, only σ‐bonds (CnH2n)


cyclopropaneC3H6

cyclobutaneC4H8

cyclopentaneC5H10

cyclohexaneC6H12

ALKANES = CnH2n+2 CYCLOALKANES = CnH2n

DIFFERENCE IN # HYDROGENS = (2n+2) ‐ 2n = 2UNITS OF UNSATURATION = 1 (1 per 2 Hs)

cycloheptaneC7H14

cyclooctaneC8H16

cyclononaneC9H18

cyclodecaneC10H20

Alkanes: Boiling/Melting Point Trends


ALKANE BOILING/MELTING POINT INCREASES WITH # CARBONS

Alkanes: Solubility


ALKANES ARE HYDROPHOBIC AND DO NOT dissolve in water (uncharged/non‐polar)

Alkanes: Density


ALKANES ARE THE LEAST DENSE OF ALL ORGANIC COMPOUNDS (weak intermolecular forces)

LIQUID ALKANES ~ 0.6‐0.8 g/mL


5‐10

carbons

“gasoline”

C5H12 to C10H22

Alkanes: Gasoline


C12H26 to C18H38

“kerosene”

12‐18

carbons

Alkanes: Kerosene


ROOFING

20‐50

carbons

“tar” or “wax”

C20H42 to C50H102

Alkanes: Tar and Wax


VASELINE

20‐50

carbons

“tar” or “wax”

C20H42 to C50H102

Alkanes: Petroleum Jelly


10,000

carbons

“polyethylene”PLASTIC BOTTLES

Alkanes: Hydrocarbon Polymers

THOSE ARE THE NAMES AND ISOMERS OF THE SIMPLE ALKANES...

BUT, HOW DO YOU NAME MORE COMPLEX

OR SUBSTITUTED ALKANES?


1. Select the longest continuous chain of carbon atoms for the basic name. (not necessarily “linear”)

2. Number the carbons in the chain from the end nearest the first branch/substituent.

3. Identify substituents (e.g. methyl, ethyl, bromo, chloro). If more than one substituent of the same kind is present, use the prefixes “di,” “tri”or “tetra.”

4. Locate the numbered carbon to which the substituents are attached.

5. Put substituents in alphabetical order (multiplier prefixes do not count).

6. Separate numbers from letters by a dash and write the whole name as one word with the basic name at the end.


IUPAC System of Naming Alkane Derivatives

Methyl & Primary Alkyl Substituents


CH3 H

CH3CH2CH2 H

CH3

CH3CH2CH2

Methyl

Ethyl

Propyl

Butyl

Methane

Ethane

Propane

Butane

1° carbon

1° carbon

1° carbon

Naming Practice – Alkanes


1. Longest continuous chain – basic name2. Number carbons 3. Identify substituents4. Number substituents5. Alphabetize substituents6. Whole name as one word (numbers/letters divided by dashes)

3 2

3

2 2 3

2 2 3

2 3



1. Longest continuous chain – basic name2. Number carbons 3. Identify substituents4. Number substituents5. Alphabetize substituents6. Whole name as one word (numbers/letters divided by dashes)

2,2,4,4‐tetramethylpentane



1. Longest continuous chain – basic name2. Number carbons – if a tie (two # options), alphabet wins3. Identify substituents4. Number substituents5. Alphabetize substituents6. Whole name as one word (numbers/letters divided by dashes)


Naming Practice – Alkanes1. Longest continuous chain – basic name2. Number carbons – if a tie, most substituted chain wins3. Identify substituents4. Number substituents5. Alphabetize substituents6. Whole name as one word (numbers/letters divided by dashes)



1. Longest continuous chain – basic name2. Number carbons – if a tie, lowest total numbering wins3. Identify substituents4. Number substituents5. Alphabetize substituents6. Whole name as one word (numbers/letters divided by dashes)

2,3,5‐trimethylhexane

OK... THAT’S NAMING BRANCHED ALKANES...

... WHAT ABOUT RING SYSTEMS?


1. Determine the number of carbon atoms in the ring.

2. Add the prefix cyclo‐ to the name of the corresponding alkane.

3. If only one substituent: not necessary to designate number.

4. If two substituents: assign C1 to substituent first in the alphabet and number in the direction that gives next substituent the lowest number.

5. If three substituents or more: begin at the substituent that leads to the lowest overall (total) numbering of the other substituents.

6. If ring is attached to a linear chain with more carbons than the ring system or if more than one ring system is attached to a single chain, name ring(s) as the substituent (cycloalkyl group).

IUPAC System of Naming Cycloalkanes



Naming Practice – Cycloalkanes1. Determine ring size – basic name with prefix “cyclo”2. 1 sub: no numbers3. 2 sub: alphabet winner/alcohol assigned C14. 3 sub: lowest overall numbering5. Name as cycloalkyl group if longer linear chain present



1‐ethyl‐3‐propylcycloheptane



2‐ethyl‐1,4‐dipropylcyclohexane

Organic Bites 2A: Main Objectives


1. Identify/name simple alkanes and cycloalkanes based on structure or condensed formula.

2. Understand the trends in boiling/melting points.3. Rationalize alkane solubility and density.4. Name alkanes/cycloalkanes with simple hydrocarbon

substituents, given a structure.5. Draw structures for alkanes/cycloalkanes with simple

hydrocarbon substituents, given a name.

CHEM 212 - Alkanes Review

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