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2202 2 Alkenes and Alkynes 2017 Filled.notebook
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May 29, 2017
Feb 124:00 PM
Alkenes and Alkynes
Lesson 2
2202 2 Alkenes and Alkynes 2017 Filled.notebook
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Alkenes (CnH2n)
• unsaturated compounds - organic compounds that contain double bonds
•General formula: CnH2n
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General formula: CnH2n-2
Alkynes (CnH2n-2)• Unsaturated compounds - organic compounds
that contain triple bonds
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Unsaturation of Hydrocarbons.
Unsaturation of Hydrocarbons
Drag the chemical structure into the boxes, then touch the degree of unsaturation.
Alkane
Alkene
Alkyne
1 2
20
10
Organic Name Structure Degree of Unsaturation
0
1
22
1
0H
HH
C CHH
HHH
HH
C C
H C HC
Unsaturated hydrocarbons are hydrocarbon chains with one or more double or triple bonds between carbon atoms. Each double bond is the equivalent of one degree of unsaturation, while each triple bond is equal to two degrees of unsaturation.
Saturated hydrocarbons are hydrocarbon chains in which all carboncarbon bonds are single covalent bonds. Or, each carbon atom is completely saturated with the maximum number of hydrogen that can be accommodated.
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Answer
Alkane
Alkene
Alkyne
0
1
2
HHH
C CHH
H
H
H
H
HC C
H C HC
1
1
2
2
0
0
Organic Name Structure Degree of Unsaturation
Answer
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Naming Scheme for Hydrocarbons
Naming Scheme for Hydrocarbons
Pull the tabs for information and labeling instructions.
Hydrocarbons are named according to the number of carbons in the longest chain, the number and location of double and triple bonds, and the location of any functional groups attached to the longest chain.
1. Number the carbons in the longest chain. 2. Circle the double/triple bonds. 3. Put a box around any important functional groups (or carbons)4. Guess and write in the systematic (IUPAC) name.5. Erase the blue shading under the line to reveal the answer.
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Ex1:Name the following structure:
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Ex 2: Name the following structureA. B.
C. D.
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Ex3: Draw a structural formula for 2-ethyl-1-pentene
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Ex 4: Draw a structural formula for each name given.a) 1pentene b) 2pentene
c) 3 hexyne d) 2octene
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e) 4octyne f) 2 butene
g) 2,2dimethyl3hexene
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Cyclic alkenes (Cycloalkenes):Rings that possess a double carbontocarbon bond. Ex 5: Draw the full structural formula, condensed structural formula, and line drawing for cyclobutene.
HH
H
HH
H
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Naming Cyclic alkenes 1. Count the number of carbon atoms in the ring.2. Name the structure the same as naming alkene but add the prefix cyclo to the alkene name.
Ex 6: Name this compound.
Answer: cyclohexene
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Ex 7: Write the possible structural isomers for following molecular formulas.a) C4H8
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b) C4H6
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Geometric Isomerism• Isomers of alkenes that differ only in the arrangement of their substituted groups
• Possible whenever each carbon of the double bond has at least one substituent
• Isomers will differ with respect to their physical and chemical properties
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• Cis – substituted groups are on the same side of the double bond
• Trans - substituted groups are on opposite sides of the double bond
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Ex 8: Draw structural formulas for and provide names for five of the possible structural isomers of C6H12.Answer:
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Alkene Properties1. React quickly with small, diatomic molecules (ie hydrogen, halogens)
F2, Cl2, Br2, I2, At2
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2. Participates in:addition reactions – converts unsaturated
hydrocarbons to saturated hydrocarbons hydrogenation – addition reactions which
convert unsaturated hydrocarbons to saturated ones by the addition of hydrogen only. Used as starting materials in the petrochemical industry for the manufacture of gasoline, plastics, etc.
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3. No rotation around a carbon-carbon double bond4. Alkenes are non-polar5. Alkenes are unsaturated 6. Structural isomers exist for all alkenes larger than propene7. LDFs only 8. As the number of carbons increase, boiling and melting points increase also
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Alkyne Properties1. As the number of carbons increase, boiling and melting points increase also.
2. Alkynes are non-polar and are soluble in non-polar solvents only.
3. LDFs only
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• 4. Alkynes are unsaturated
• 7. React in addition and hydrogenation reactions
• 5. No rotation around carbon-carbon triple bond.
• 6. Structural isomers exist for alkynes larger than propyne
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PHYSICAL PROPERTIES OF CYCLOALKANES AND CYCLOALKENES
Cycloalkanes (and cycloalkenes) have higher boiling points and densities than their corresponding alkane (alkene) with the same number of carbons because of their more compact structure.ie: cyclopentane will have a higher boiling point than pentane.
Carbon Range Boiling point State
C1 C4 164 to 0.5 Gas
C5 C16 30 to 375 Liquid
C17 > 375 to 515 Wax like Solid
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QUESTION:1. Construct a table, a) list alkene names, boiling points and # of electrons.
Alkenes Boiling Point # of electrons
Ethene 103.9 16
Propene 47.0 24
1butene 6.3 32
1pentene 30.0 40
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b) list alkyne names, boiling points and # of electrons.
Alkynes Boiling Point # of electrons
Ethyne 81.8 14
Propyne 23.3 22
1butyne 8.6 30
1pentyne 40.0 38
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c) For the homologous group with two carbons, listing boiling point and # of electrons.
compounds Boiling Point # of electrons
Ethane 88.5 18
Ethene 103.9 16
Ethyne 81.8 14
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2.a) Which would you predict to have the lower boiling point and why?
Would predict ethyne having the lowest boiling point since it has the lowest number of electrons therefore the lowest LDF.
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b) Suggest a reason why it does not.Another factor that affects the strength of LDF is the shape of the molecule. The closer the molecules can get together, the stronger the LDF will be. Ethyne C 2H2 is a linear molecule about each carbon.H C = C H
Ethene is trigonal planar about each carbon.
Ethane is tetrahedral about each carbon
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