Chapter 4 Flashcards
Describe the structure of Alkenes
The two carbon atoms of the double bond and the four atoms bonded to them line in a plane, with bond angles of roughly 120
According to the orbital overlap model, a double bond consists of one _______ bond formed by the overlap of sp2 hybridized orbitals AND one _______ formed by the overlap of parallel 2p orbitals
σ
π
If you rotate about a π bond, it does what? What does this restriction mean for C-C conformations?
Rotation removes the overlap in the 2p orbitals thus breaking the π bond. Because of restricted rotation about a C-C double bond, groups on the carbons of a double bond are either cis or trans isomers to each other, not staggered or eclipsed conformations
Is the cis or trans conformation around a C=C bond in an alkene more stable?
Due to the nonbonding interaction strain (steric) between alkyl (heavy) groups on the same side of the double bond, a trans alkene is more stable than an isomeric cis alkene
Compare usage of the cis-trans system and E-Z system for determining alkene configurations
The cis-trans system is generally suitable for alkenes with one non-hydrogen group attached to each of the C=C carbons
The E-Z system is suitable for all alkenes, including those with 3 or four non-hydrogen groups.
Draw trans-3-hexene and cis-3,4-dimethyl-2-pentene, which would be E and which would be Z?
What is the different between a Z (zusammen) and E (entgegen) configuration? Which one is “cis” and which is “trans”?
To determine if a group on a C=C bond is higher or lower, it is assigned a priority. What is the first priority rule?
“how chilly the nights, oh such clear bright ice!”
To determine if a group on a C=C bond is higher or lower, it is assigned a priority. What is the second priority rule if the bonded atoms are all of similar atomic number?
To determine if a group on a C=C bond is higher or lower, it is assigned a priority. What is the third priority rule (HINT) it does not related to ranking but is related to the kinds of bonds present
The configuration of the double bond in cyclo________ through cyclo_________ MUST be ________.
Propene
Heptene
Cis
These rings are not large enough to accommodate a trans double bond
__________ is the smallest cycloalkene that can accommodate a trans double bond
Cyclooctene
For an alkene with n C=C bonds that can show cis-trans isomerism, ________ cis-trans isomers are possible
2n
Draw trans,trans-2,4-Heptadiene
Draw trans,cis-2,4-Heptadiene
[IUPAC] use the infix _______ to show the presence of a C=C bond. Number the parent chain to give the first C of the double bond the _________ number.
-en-
lower
[IUPAC] For a cycloalkene, number the atoms in the ring beginning with . . .
the two carbons of the double bond
[IUPAC] When naming alkenes, the parent chain is the longest chain . . .
containing the entire C=C bond EVEN IF a different chain with NO C=C is longer
[IUPAC] Name the following.
1-hexene
4-methyl-1-hexene
2-ethyl-3-methyl-1-pentene
[IUPAC] The presence of multiple double bonds is indicated by . . .
The appropriate suffix (-diene, -triene) and associated location number
[IUPAC] Name the following.
2-pentene
2-methyl-3-hexene
[IUPAC] Name the following.
3-ethyl-1-butene
5-methyl-1,3-hexadiene
[IUPAC] use the infix _______ to show the presence of a C≡C bond. Number the parent chain to give the first C of the triple bond the _________ number.
-yne-
lower
[IUPAC] Name the following.
3-methyl-1-butyne
6,6-dimethyl-3-heptyne
The functional group of an alkyne is a ________. Consisting of . . . ?
C≡C triple bond
- one σ bond between overlapping sp orbitals
- 2 π bonds formed by overlap of sets of parallel 2p orbitals
Alkenes and Alkynes are ________ compounds. The only attractive forces between their molecules are ____________
nonpolar
dispersion forces
Alkenes/Alkynes that are liquid at room temperature are _____ dense than water. They are _______ in water.
less
insoluble
Since s orbitals are closer to the nucleus than p orbitals, s orbitals hold a ______ charger better. Thus, sp carbon is ________ electronegative than sp2 carbon, which is _______ electronegative than sp3 carbon
negative
more
more
Rank ethane, ethylene, and acetylene by increasing acidity based on how the % s character impacts conjugate stability
For carbocations, the electron density of the carbon bearing the negative charge ___________ as its hybridization changes from sp3 -> sp2 -> sp and electronegativity ___________
decreases
increases
The ______ the e- density of a carbocation, the ______ stable the compound.
lower
more
What is the major difference between the chemistry of Alkenes and Alkynes which interacting with strong bases?
The H atom of a terminal alkyne is sufficiently acidic (low pKa) that it can be removed by a strong base to create an alkyne anion
Keq = __________
pKa1 is ALWAYS the _______ acid, meaning its _____ in value
Keq = 10pKa2 - pKa1
stronger acid, lower
