Week 10-11 Flashcards
It is sometimes called olefin
Alkene
Alkene is sometimes called
Olefin
An alkene, sometimes called an olefin, is a hydrocarbon that contains a
Carbon-carbon double bond
General formula of alkene
CnH2n
The double bonds in alkenes are higher in ____ than single bonds and are more_____
energy; reactive
It is the smallest, simplest alkene
Ethene
Ethene is a_____ and the angle between its bonds is approximately _____
planar; 120°
The ___ bonds are ______ stronger in ____than in ethane because the ___ bond draws electron density away from the carbon, which draws electron density away from the hydrogens
C-H
Stronger
Ethene
Pi
It is an orange pigment and vitamin A precursor
β-Carotene
(True or False)
Cycloalkenes are named similarly, but because there is no chain end to begin from, we number the cycloalkene so that the double bond is between C3 and C4
False
(C1 and C2)
The ______ substituent has as low a number as possible
first
(True or False)
It is necessary to indicate the position of the double bond in the name because its always C3 and C4
False
(not necessary; C1 and C2)
=CH2 substituent is called a
methylene group
H2C=CH- substituent is called a
vinyl group
H2C=CHCH2- substituent is called an
allyl group
is used to help draw chemical structures in organic chemistry
Degree of unsaturation or Index of Hydrogen Deficiency (IHD)
each ring or double bond in a molecule corresponds to a loss of ______hydrogens from the alkane formula CnH2n+2.
two
If IHD is equal to 0
single bonds only; no ring structures
If IHD is equal to 1
1 double bond or 1 ring
If IHD is equal to 2
1 triple bond, 2 double bonds, 2 rings, or 1 double bond and ring
If IHD is equal to 3
2 double bonds and ring
If IHD is equal to 4
benzene ring
The _____ is used to calculate the number of rings and pi bonds there is/are in a molecule.
IHD
(True or false)
cis and trans isomers of alkenes do not have the same stability
true
caused by crowding of two alkyl groups on the
same side of a double bond
steric strain
cis isomers is ____ than trans isomers
less stable
(True or false)
The greater the number of attached alkyl groups, the lesser is the alkene’s stability
false
(greater)
a stabilizing interaction between the C=C
π bond and adjacent C – H sigma bonds on substituents.
hyperconjugation
(True or false)
a bond between an sp2 carbon and an sp3 carbon is somewhat stronger than a bond between two sp3
carbons
true
first 3 members (C2 to C4) are _____ in nature
gaseous
next 14 members (C4 to C18) are______
liquids
greater than C19 are
solids
alkenes are colorless and odorless (except_____, a colorless gas with a faintly sweet odor)
ethene
Alkenes are insoluble in water but completely soluble in nonpolar solvents such as benzene
true
(True or false)
Alkene’s boiling point increases with decreasing number of C atoms (increasing molecular weight)
false
(increasing)
(True or False)
as carbon increases, LDF strength increases
true
In alkenes, boiling point ___ in increasing branching
decreases
(true or false)
cis-isomers have a greater melting point than trans-isomers
false
(lower)
1,2-Elimination reactions is also called
β-Eliminations
is an empirical rule used to predict the major
products of elimination reactions
Zaitsev’s rule
It states that in an elimination reaction, the major product is the more stable alkene with the more highly substituted double bond
Zaitsev’s rule
E2 rxn is
elimination bimolecular
occurs when a migrating group with its pair of electrons moves from an adjacent carbon to the
carbon bearing the positive charge
carbocation rearrangement
The carbon that loses the migrating group acquires the ______ charge
positive
Rearrangement results to the formation of a ____________
more stable carbocation
in which a hydrogen, with its pair of electrons, is the migrating group
hydride shift
in which the alkyl group is the migrating group.
alkyl shift
