Lesson 3: Alkenes Flashcards
Types of hydrocarbons
Saturated hydrocarbons
Unsaturated hydrocarbons
Do not contain the maximum number of hydrogen atoms.
Unsaturated hydrocarbons
Contain carbon-carbon double bonds.
Alkenes
General formula of alkenes
CsubnHsub2n
In alkenes, molecule is ___________ because the carbon and hydrogen atoms all lie in the same plane.
Flat or planar
Hybridization of alkenes
Hybrid Orbitals
Molecular Orbitals
Result from combinations of orbitals within a given atom, either prior to or as bonding with another atom takes place.
Hybrid Orbitals
Result from combinations of orbitals between atoms as bonding takes place to form molecules.
Molecular Orbitals
The sp2 orbitals are arranged in a __________ around the central carbon atom, with bond angles of 120°.
Trigonal planar shape
The unhybridized P orbital is ___________ to the plane.
Perpendicular
End-on-end overlap of the sp2 orbitals to make a ___________.
Sigma bond
Side-to-side overlap of the unhybridized P orbitals to make a __________.
Pi-bond
Because of the pi- bond, ___________ is not possible around carbon-carbon double bonds.
Free rotation
Since each carbon in the double bond is trigonal planar in shape, the entire ethylene molecule is a ___________, with the atoms separated by bond angles of 120°
Flat molecule
In longer Alkyl chains, the additional carbon atoms attached to each other by __________.
Single covalent bonds
Each carbon atom is also attached to a sufficient hydrogen atoms to produce a total of __________ about itself.
Four single covalent bonds
Existence of isomers that differ in the orientation of their atoms in space.
Stereoisomers
An isomers in which the two substituents (the methyl and ethyl groups) are on the same side of the double bond, is called _________.
Cis isomer
An isomers with two non hydrogen substituents on opposite sides of the double bond is called ________.
Trans isomer
If more than two substituents are attached to the carbon atoms of a double bond, the cis and trans system _____________.
Cannot be used
-bisected vertically through the double bond.
E-Z system
If the two atoms are in the cis position, the arrangement is ___.
Z
Z for German zusammen meaning ________.
Together
If the atoms or groups are in the trans position, Tha arrangement is ___.
E
E for German entgegen, meaning ________.
Opposite
System on which the organic chemists utilize to circumvent problems caused by arbitrary nomenclature.
International Union of Pure and Applied chemistry
The suffix for alkene
-ene
Rules of the IUPAC system for naming alkenes.
- Name the parent hydrocarbon.
- Number the carbon atoms in the chain.
- Write the full name.
A cyclic unsaturated hydrocarbon with one or more carbon-carbon double bonds within the ring system.
Cycloalkenes
Alkenes substituents are called __________
Alkenyl groups
A noncycli hydrocarbon substituents in which a C-C double bond is present.
Alkenyl grouos
Most frequently encountered alkenyl groups:
-methylidene(one-carbon)
Common name: methylene
-ethynyl (two-carbon)
Common name: vinyl
-2-propenyl (three-carbon)
Common name: allyl
In physical state of alkenes, alkenes are ________ and ________ in nature.
Colorless and odorless
________ is an exception because it is a colorless gas with a faintly sweet odor.
Ethene
The first three members of the alkene group are __________.
Gaseous in nature
The next 14 members of the alkene group are _________.
Liquids
The remaining alkenes are ________.
Solid
The alkenes are insoluble in water due to their _________ characteristics.
Nonpolar
Completely soluble in nonpolar solvents
Benzene
Ligroin
The boiling points of the compounds increase as the number of ________ into he compound increases.
Carbon atoms
The boiling point of alkenes and alkanes are ___________.
Almost similar
The boiling point of straight-chain alkenes is more than ___________ alkenes just as in alkenes.
Branched-chain
The melting points of these double-bonded compounds depends upon the __________ of the molecules.
Positioning
The melting point of alkenes is similar to __________.
Alkanes
___________ molecules have a lower melting point than ________ as the molecules are packed in a U-bending shape.
Cis-isomers, trans isomers
Alkenes are weakly _______ just like alkanes
Polar
Alkenes are slightly more ________ than alkanes due to the presence of double bonds.
Reactive
The pi electrons which make up the double bonds can easily be removed or added as they are __________ held.
Weakly
Naturally occurring alkenes
Ethene
Pheromone
Terpenes
Produced naturally by all higher plants from the amino acid methionine and is a plant growth regulator.
Ethene
Compound used by insects (and some animals) to transmit a message to other members of the same species.
Pheromones
Organic compounds whose carbon skeleton is composed of two or more 5-carbon isoprene structural units.
Terpenes
Other example of Alkenes
Propylene
B-carotene
ą-pinene
Produced primarily as a by-product of petroleum refining and of ethylene production by steam cracking of hydrocarbon feedstocks.
Propylene
The orange pigment that gives carrots their color. It is an important dietary source of vitamin A and is thought to offer some protection against certain types of cancer.
B-carotene
An organic compound of the terpene class. It is found in the oils of many species of many coniferous trees, notably the pine.
ą-Pinene
Alkenes are generally prepared through ____________, in which two atoms on adjacent carbon atoms are removed, resulting in the formation of a double bond.
B elimination reactions
Alkenes can be prepared by 3 methods
Dehydration of alcohols
Dehydrohalogenation of Alkyl halides
Dehalogenation of alkenes
A molecule of water is eliminated from an alcohol molecule by heating the alcohol in the presence of a strong mineral acid.
Dehydration reactions
The mechanism of dehydration reaction
- Protonation of the alcohol
- Dissociation of the oxonium ion.
- Deprotonation of the carbocations.
-Involves in the loss of a hydrogen and a halide from an Alkyl halide (RX).
-normally accomplished by reacting the Alkyl halide with a strong base, such as sodium ethoxide.
Dehydrohalogenation of Alkyl halides
Mechanisms of Dehydrohalogenation of Alkyl halides
- A strong base removes a slightly acidic hydrogen proton from the Alkyl halide via and acid-base reaction.
- The electrons from the broken hydrogen-carbon bond attracted toward the slightly positive carbon atom attached to the chlorine atom.
Main reasons for the reactivity of alkenes.
Weak bond
Electron density
Pi bond is a __________, unlike sigma bond that isn’t easily break.
Weak bond
Alkene attract electrons
Electron density
The most characteristic reaction of alkenes
Addition to carbon-carbon double bond
Addition reaction of alkenes
Markovnikov’s rule
Regioselective reaction
In the addition of HX or H20 to an alkene, hydrogen adds to the carbon of the double bond having the greater number of hydrogen.
Markovnikov’s rule
A reaction in which one direction of bond forming or bond breaking occurs in preferences to all other directions.
Regioselective reaction
Alkenes that have double bonded carbon atoms bearing the same ligands
Symmetrical alkenes
Alkenes that have double bond carbon atoms bearing different ligands.
Unsymmetrical alkenes
Reaction of alkenes: Addition
A. Addition of hydrogen halides
B. Addition of water
C. Addition of bromine and chlorine
D. Hydroxylaction (oxidation)
E. Hyrogenation
Formation process of monomers by repeated addition reactions of many unsaturated alkene molecules.
Addition polymerization
________ is a method of oxidatively cleaving alkenes or alkynes using ozone (O3).
Ozonolysis
This reaction is often used to identify the structure of unknown alkenes, by breaking them down into smaller, more identifiable species.
Oxidative cleavage of alkenes
Applications and uses of alkenes
-polyethylene hip replacement.
-shatterproof acrylic plexiglass
-PVC piping for drains.
Commercial use of ethylene;
Ripening of climacteric fruits
-bananas
-tomatoes
-avocadoes
-mangoes
-papayas
-persimmons
-honeydew melons
Applications of alkenes
-ripening fruits and vegetables.
-1-octene for lemon oil
-Ocatadecene (C18H36) found in fish liver.
-Butadiene in coffee.
-lycopene and carotene give the attractive red, orange, and yellow colors to fruits and vegetables.
