Upload
others
View
3
Download
0
Embed Size (px)
Citation preview
Organic Chemistry
February 18, 2014
What does “organic” mean?
• “Organic”
– Describes products
– Grown through “natural” biological process
– Without “synthetic” materials
• In the 18th century
– Produced by a living system
– Could not be produced in a lab
“Organic”
• In 1828– German chemist: Friedrich Wohler
– Reacted two inorganic compounds
– Obtained urea (organic compound)
Our Definition
• Organic Compound– A molecular compound containing carbon
• Not including (CO(g), CO2(g), HCN(g))
“Organic Chemistry”
• Organic Chemistry
– Is the study of compounds in which carbon is the principle element
– Example: animals, fossil fuels, plants
Carbon
• Atom can form four bonds– Four valence electrons
– Bond angle: 109.5o
• Atoms can bond together to form– Chains, Rings, Spheres, Sheets, Tubes
• Form combinations of bonds– Single, Double, and Triple bonds
• Carbon chains are the backbone of many molecules
Hydrocarbons• A compound containing only carbon and
hydrogen atoms
• There are two main classes: aliphatic and aromatic
Hydrocarbons
• Aliphatic hydrocarbons
– A compound that has chains or rings of carbon
• Does not include aromatics
• Aromatic hydrocarbons
– Compound based on a ring of six carbons
– Formula: C6H6
– All six bonds: intermediate between single and double bonds
Alkanes
• Saturated hydrocarbon– Only has single bonds between carbons
• General Formula
–CnH2n+2
First 10 AlkanesCH4 methaneC2H6 ethane C3H8 propane C4H10 butane C5H12 pentane C6H14 hexaneC7H16 heptaneC8H18 octaneC9H20 nonane
C10H22 decane
Prefix: based on the number of carbons in the longest chainSuffix: “ane” ending
Diagrams
• Expanded Structural Diagrams
– The normal structures of a few alkanes
methane propane
hexaneC
H
H
H
H C C C
H
H
H
H
H
H
H
H
C C C
H
H
H
H
H
H
H H
H
H
H
H
H
H
CCC
Building/Drawing Alkanes
• C2H6
• C3H8
• C5H12
Structural Isomers
• Structural Isomers
– Compounds with the same chemical formula
– Have the same molecular mass
– Different arrangements of atoms
– Physical and Chemical properties may be different
C C C
H
H
H
H
H
H
H
C C
H H
H
HH
C C C
H
H
H
H
H
H
C
H
H
C
HH H
H
Alkyl Groups• One (or more) carbon branches attached to
the main chain of the hydrocarbon
• Naming
– Drop the –ane of the corresponding alkane
– End with –yl
• General Formula: CnH2n-1
• Type of substituent group
– Anything that replaces hydrogen in an organic molecule
Alkyl Group
• Carbon chain added to the parent chain– methyl
– ethyl
– propyl
– butyl
– pentyl
– hexyl
• Follow the same prefixes as the parent chain
• End in “yl”
Naming Alkanes
1. Identify the longest continuous carbon chain– BE CAREFUL! It may not be in a straight line
Longest chain is 5 carbon atoms
2. Number the carbon atoms– Start with the end nearest to the substituent
group
CH2 CH2 CH CH3
CH3CH3
CH2 CH2 CH CH3
CH3CH3
1234
5
Naming Alkanes
3. Name the chain by adding “-ane”– pentane
4. Name the substituent group– Methyl
5. Attach the name of the group as a prefix
AND the attached carbon number– 2-methylpentane
CH2 CH2 CH CH3
CH3CH3
1234
5
Naming Alkanes
6. If two or more of the same group occur– Use prefixes: di, tri, tetra, etc.
– Locate their position on the main chain
– Separate numbers by commas
– Separate words by hyphens
2,3-dimethylpentane
CH2 CH CH CH3
CH3CH3
CH3
12345
Naming Alkanes
7. If different groups are present
– Arrange in alphabetical order
– Use numbers to indicate their position
5 - ethyl - 2,3,6 - trimethyloctane
CH3 CH CH CH2 CH CH CH2 CH3
CH3
CH3
CH2
CH3
CH31 8
Alkyl Halides
• An alkane in which one or more hydrogen atoms have been replaced by one or more halogen atoms
F- fluoro Cl- chloro Br- bromo I- iodo
• Other common groups
NO2- nitro NH2- amino
Naming Alkyl Halides
• Use the same rules as naming alkanes with branches
1-bromo-3,4-dimethylpentane
1,1,2-trichloro-3-methylpentane
4-ethyl-2-fluoroheptane
CH2 CH2 CH CH
CH3
CH3
CH3
Br
CH CH CH CH3
CH2 CH3
ClCl
Cl
CH3 C H
F
C H2 C H
C H2 C H 3
C H 2
C H 2
C H 3
Drawing Organic Molecules
• Expanded Structural Diagrams– Shows all bonds between atoms
• Condensed Structural Diagrams– Combine carbon atoms and the hydrogens bonded
• Line Diagrams– Only show carbon bonds
– Assumed hydrogens are attached appropriately
CH3CH2CH2CH2CH3
C C C
H
H
H
H
H
H
H
C C
H H
H
HH
Alkenes• Contain at least one carbon double bond
(C=C)
• Unsaturated
– Less than the maximum quantity of hydrogen
• More reactive than alkanes
• General Formula: CnH2n
Examples
– Ethene C2H4
– Propene C3H6
– Butene C4H8
1-butene 2-butene
C C
H
H
H
H
C C
HH
H CH3
C C
HH
H CH2CH3
C C
HH
CH3CH3
but-1-ene but-2-ene
Naming Alkenes
• General Rules for Naming
1. All alkane rules apply
2. Change the ending to “-ene”
– Must include double bond(s) in the chain
3. Start numbering carbons closest to double bond
Naming Alkenes
4. Include the number of the bonded carbon– Either in front of chain name or before suffix
5. More than one double bond– Use prefix before suffix
– di, tri, tetra, etc.
1, 3 pentdiene pent-1,3-diene
Geometric Isomers
• Carbon-carbon double bonds
– Not free to rotate (sigma + pi bonds)
• Two structures can exist
• Example: 2-butene
C C
HH
CH3CH3
C C
H
CH3
CH3
H
cis-2-butene trans-2-butene
Geometric Isomers
“cis”
– Latin for “on this side”
– C or “sis”
“trans”
– Latin “across”
– “trans”atlantic
cis-1,2-dichloroethene(mp = -81OC; bp = 60OC)
C C
H
Cl Cl
H
C C
H
H Cl
Cl
trans-1,2-dichloroethene(mp = -81OC; bp = 48OC)
Alkynes• Contain at least one carbon triple bond
• Unsaturated
– Less than the maximum quantity of hydrogen
• More reactive than alkanes (and alkenes)
• General Formula: CnH2n-2
Naming Alkynes
• General Rules for Naming
1. All alkane/alkene rules apply
2. Change the ending to “-yne”
– Must include triple bond(s) in the chain
3. Start numbering carbons closest to triple bond
Naming Alkynes
4. Include the number of the bonded carbon– Either in front of chain name or before suffix
5. More than one triple bond– Use prefix before suffix
– di, tri, tetra, etc.
2-butyne 4-chloro-1-butyne
but-2-yne 4-chlorobut-1-yne
CH3 C C CH3 CH2 CH2 C C H
Cl
Cyclic Aliphatics
• Carbon atoms can also be arranged in rings
• Named after the corresponding “open chain”
– Same rules apply for alkanes, alkenes, alkynes
• Prefix cyclo
• Substituents can be named after based on position
CH2
CH2 CH2
CH2CH
CH
CH2 CH2
CH2
cyclobutane cyclopentene 3-ethylcyclopentene
CH
CH
CH2 CH2
CH CH2 CH3
Cyclic Aliphatics
• For convenience, you can draw the corresponding polygon for each size of carbon ring
– Triangle (3 carbon), square (4 carbon), etc.
• It is understood that the appropriate number of hydrogens are attached
cyclopentene 1,2,3-trimethylcyclohexane
CH3
CH3
CH3
Structural Isomers• The number of structural isomers increase as
the number of carbon atoms increase
Properties of Hydrocarbons
Physical Properties of Hydrocarbons
• Since C and H have similar electronegativities, there are covalent bonds– Generally non-polar molecules
• The main intermolecular force is van der Waals forces. These are weak, making the compound easy to separate.
• Van der Waals forces: the attraction of electrons of one molecule for the the nuclei of another molecule
• As the compound gets larger in size, the strength of VDW forces increases, leading to higher MP and BP
Fractional Distillation
Reactions of Hydrocarbons
Reactions of Alkanes
• ALL hydrocarbons undergo COMBUSTION REACTIONS, making them useful fuels
• Complete Combustion: chemical reaction that involves a compound reacting with O2 to produce carbon dioxide, water and thermal energy
Reactions of Alkanes
• Alkanes are generally unreactive
– Single C-C bonds are hard to break
• Primarily undergo SUBSTITUTION REACTIONS
– Reaction that replaces a hydrogen atom with another atom or group of atoms
Reactions of Alkanes
• H can be substituted by a halogen atom
– Halides (Br2) or Hydrogen halides (HBr)
– Form ALKYL HALIDES
• Usually requires heat or UV light
– Reactions involving F2 are vigorous
Reactions of Alkanes
• As the reaction proceeds:
• Additional bromines can be added resulting in a mixture of brominated products
– Separated by fractional distillation
Reactions of Alkenes and Alkynes
• Due to the presence of multiple bonds– Alkenes/Alkynes are MORE REACTIVE than
alkanes
• For example, reactions with Br2 are vigorous at room temperature– Alkanes require heat or UV light to react
• Undergo ADDITION REACTIONS– Atoms are added to the compound without loss of
hydrogen
• There are FOUR types of ADDITION reactions
• Classified by the type of compound being reacted
1. Halogenation – reaction with halogen
Reactions of Alkenes and Alkynes
2. Hydrogenation – reaction with H2
Reactions of Alkenes and Alkynes
3. Hydrohalogenation – reaction with hydrogen halides (HX)
Reactions of Alkenes and Alkynes
4. Hydration – reaction with water
Reactions of Alkenes and Alkynes
Markovnikov’s Rule
• When a hydrogen halide or water molecule reacts with an Alkene,
– the hydrogen atom will generally bond to the carbon atom in the multiple bond that has the most hydrogen atoms already bonded to it
Aromatic Hydrocarbons
• Aromatic hydrocarbons are benzene or a compound that contains a benzene ring
• Benzene has the formula: C6H6
CH5
CH4
CH6
CH3
CH1
CH2
Aromatic Hydrocarbons
• Electrons involved in the double bonds are equally shared among the 6 carbons
• Benzene can be thought of as a hybrid of two “resonance forms”
• A common way to represent benzene
Aromatic Hydrocarbons
General Rules for Naming
• The benzene ring is usually considered the parent chain
1. If an alkyl group is attached to benzene, the compound is named alkylbenzene
Cl
Br
F
NO2
fluorobenzene chlorobenzene
bromobenzene nitrobenzene
Aromatic Hydrocarbons
2. If more than one alkyl group is attached to the benzene ring, number each using the lowest combination of numbers (IUPAC)
Cl
Cl
Cl
Cl
1,2-dichlorobenzene 1,3-dichlorobenzene
1 1
22
3
4
5 5
4
66
3
Aromatic Hydrocarbons
• Occasionally, benzene groups are found as a substituent to more complex hydrocarbon chains.
• The benzene is called phenyl
3-chloro-2-methyl-4-phenyl-2-pentene
C C CH CH3
CH3
CH3 Cl
Ortho, Meta, Para
• Alternate system using relative position
Example: diethylbenzene
o-diethylbenzene m-diethylbenzene p-diethylbenzene
o = ortho m = meta p = para
Practice
Properties of Aromatics
• Most are liquids at room temperature
– Some are crystalline solids
• Symmetrical structures
– Non-polar (unless it has an electronegative substituent)
– Generally insoluble in water
Reactions of Aromatic Compounds
• Unique bonding makes the bond strength greater than alkenes
• Much less reactive than alkenes
• Undergoes SUBSTITUTION Reactions
– Like alkanes
Reactions of Aromatic Compounds
• Further reactions with halogens (Br2) can result in additional substitutions. In theory, the bromine can replace any hydrogen.
Substitution Reactions with Benzene
Difference with 6 carbon rings