Unit 2Introduction to Hydrocarbons

Differences between organic and inorganic compounds:

1. Organic compounds are mostly covalent molecules where most inorganics are ionic

2. Most organics don’t dissolve in water and most inorganics do

3. Organic compounds decompose on heating easier than inorganics

4. Organic reactions are much slower (min, hours, days) than inorganic reactions (seconds)

Fun Facts (Don’t have to Copy)

More than 18 Million organic compounds [with 10,000 new ones discovered each year]

1.7 Million inorganic compounds so about 85% of compounds are organic

2 Reasons for the abundance of organic compounds:

Carbon atoms bond to each other to form long chains(up to 200 carbons)Catenation – the ability of an element to bond

to itself

The same number of carbon atoms can rearrange to form different structures (isomers)Isomer – compounds with the same molecular

formula but different structures

Isomer Example

C5H12

C C

-C-C-C-C-C- -C-C-C-C- -C-C-C-

C

How Carbon Bonds

C ground state is 2s22p2 but bonds as *2s12p3 giving 4 sp3 hybrid orbitals

Hybrid orbitals – orbitals of equal energy formed by mixing orbitals of different energies

Hybridization – the mixing of orbitals of different energies to give orbitals of equal energy 

How Carbon Bonds

Carbon’s 4 covalent bonds form a tetrahedron (109.5° bond angle)

Hydrocarbons!

Hydrocarbons – compounds containing only hydrogen and carbon

Alkanes – hydrocarbons that have all C-C single bonds

Naming# of C

Name Structural Formula

Condensed Formula

Molecular Formula

1 Methane -C- CH4 CH4

2 Ethane -C-C- CH3CH3 C2H6

3 Propane -C-C-C- CH3CH2 CH3 C3H8

4 Butane -C-C-C-C- CH3(CH2)2 CH3 C4H10

5 Pentane -C-C-C-C-C- CH3(CH2)3 CH3 C5H12

6 Hexane -C-C-C-C-C-C- CH3(CH2)4 CH3 C6H14

7 Heptane -C-C-C-C-C-C-C- CH3(CH2)5 CH3 C7H16

8 Octane -C-C-C-C-C-C-C-C-

CH3(CH2)6 CH3 C8H18

9 Nonane -C-C-C-C-C-C-C-C-C-

CH3(CH2)7 CH3 C9H20

10 Decane -C-C-C-C-C-C-C-C-C-C-

CH3(CH2)8 CH3 C10H22

Naming*Know roots and endings*

Each step, you add a CH2 group

Homologous Series – a series of compounds where each member differs from the next by a constant unit (CH2)

Members are called homologous Since alkanes are homologous –

we can write a General Formula = CnH2n+2

Naming

Alkanes are Saturated Hydrocarbons – hydrocarbons where each C has 4 single covalent bonds (no more atoms can be added)

Alkenes Alkenes – hydrocarbons with one C=C double

bond – sp2 hybridization on the 2 C atoms in the double bond.

Ethene C=C CH2CH2

C2H4

Propene C=C-C CH2CHCH3

C3H6

Butene C=C-C-C CH2CHCH2CH3

C4H8

Octene C=C-C-C-C-C-C-C- CH2CH(CH2)5CH3

C8H16

Ways to Show Organics

Line Bond Form

Ball and Stick Form

Space Filling Model

Skeletal Form

Structural Formula

AlkenesAlso a homologous series General

Formula CnH2n

Unsaturated hydrocarbons – have C-C multiple bonds which can be broken to add more atoms to the molecule

H H H H

Ex: C=C + H2 H-C -C-H

H H H H

Alkynes Alkynes – hydrocarbons containing a C = C

triple bond – sp hybtidization

Ethyne -C=C- CHCH C2H2

(acetylene)

Propyne -C=C-C- CHCCH3

C3H4

Butyne -C=C-C-C- CHCCH2CH3 C4H6

Heptyne -C=C-C-C-C-C-C- CHC(CH2)4CH3

C7H12

General Formula = CnH2n-2

Alkadienes Alkadienes – hydrocarbons containing two

C=C double bonds

Butadiene -C=C-C=C- CH2(CH)2CH2

C4H6

Pentadiene -C=C-C=C-C- CH2(CH)3CH3

C5H8

Heptadiene -C=C-C=C-C-C-C- CH2(CH)3(CH2)2CH3

C7H12

General Formula = CnH2n-2

Alkadienes3 placements for the two double bondsConjugated double bonds (most

common) – two double bonds separated by one singe bond

Isolated double bonds – two double bonds separated by more than one single bond

Allenes – hydrocarbons that have two consecutive double bonds

The first 4 Series of hydrocarbons are Aliphatic HydrocarbonsAliphatic hydrocarbons –

hydrocarbon where carbon atoms bond together in open chains

Arenes Aromatic Hydrocarbons – hydrocarbons

containing rings of 6 carbon atoms joined by alternating single and double bonds

Simplest aromatic hydrocarbon = benzene

Arenes

All bonds are actually identical (C-C and C=C “mixed”)

Can also be shown as

Arenes

We use The e-‘s are actually shared by all 6

carbons and move freely around the ring (delocalized)This makes benzene behave like

saturated hydrocarbons

Resonance

Compounds like these are resonance hybrids (compounds that can be represented by more than one Lewis structure)

General Formula = CnH1/2n+3

Resonance examples

IUPAC Naming Rules1. Name the longest chain (the parent chain) first.

2. Label the chain to give the lowest numbers to groups or bonds. Priority C=C then C=C You give the number for the carbon where the multiple bond begins. (Separate numbers and words with a hyphen, and numbers and numbers with a comma).

6 5 4 3 2 1

C-C-C-C=C-C 2 –hexene

C-C-C=C-C-C-C 3 – heptyne

IUPAC Naming Rules

3. Give the numbers for any attached groups for the carbons they are attached to, a number for each attached group. Use the number with the groups name. [in front of “main” chain]

a) If more than one of any group = di-, tri-, tetra-, penta-, hexa-, etc.

b) Group Names: F = fluoro I = iodo

Cl = chloro OH = hydroxo

Br = bromo NO2 = nitro

IUPAC Naming Rulesc. If there is more than one group attached, the names are listed in alphabetical order (ignore prefixes) in front of the “main” chain

d. If the numbers for the side groups are the same from either side of the chain, # from the side that gives the lowest # to the first group in the alpha order.

Summary

Hydrocarbons (straight chains)Locate and name attached groupsLocate multiple bonds (priority for

numbering)Name base/parent chain

IUPAC Naming Rules

4. Branched chainsLongest continuous chain containing

any multiple bonds (if present)

# to give multiple bonds lowest numbers (priority)

Name side groups (alphabetical order)

IUPAC Naming Rules

1-chloro-3,5 - dimethylbezene

5. BenzeneNumber starting with a C bonded to an

attached group and then continue around the ring

Use the lowest set of #’s possible

IUPAC Naming Rules

1,3 – dibromo – 2 – fluorobenzene

IUPAC Naming Rules

c. If there are just two of the same group attached, we can use the following terms to simplify the bonding positions

Ortho = 1, 2 bonding positionMeta = 1, 3 bonding positionPara = 1, 4 bonding position

O,M, P

Isomer Practice

Isomers – compounds having the same molecular formula but having different structures

Example: C5H11Cl

Draw all isomers by moving Cl (we are only going to use straight chains for C’s)

Isomer Practice

Cl

C – C – C – C – C

Cl

C –C – C – C – C

Cl

C – C – C – C – C

Isomer Practice

C4H8Cl2

Isomer Practice

Try C4H8ClI, C4H7I3, C5H10FBr, and C4H7F2Br