Exam 2 Flashcards
What is an alkene?
Contain one or more Carbon-Carbon double bonds
What is an alkyne?
Contain one or more Carbon-Carbon triple bonds
What is an alkene classified as?
Unsaturated hydocarbons
What is an alkyne classified as?
Unsaturated hydrocarbons
What does sigma form a bond between?
Overlapping sp-sp orbitals
What does a side to side overlap between 2p orbitals form?
A pi bond
Why do you start a curved arrow on a pi bond?
It has the most energy to react because its electrons are stored in unhybridized orbitals
What is the relationship between bond length and sp orbitals?
When S character increases, bond length gets shorter because the spherical shape is shorter than that of the elongated P orbital
What is an isomeric alkene?
Differ in the position of the double bonds.
What is a constitutional isomer?
Molecules with the same molecular formula, but different in atom connectivity.
What are stereoisomers?
Compounds with identical connectivity that differ in the spatial arrangement of their atoms.
What is a sterocenter?
An atom is a stereocenter when the exchange of 2 bonded groups gives stereoisomers.
What is this substituent group?
Vinyl
What is this substituent group?
Allyl
What is this substituent group?
Isopropenyl
How do you assign the highest priority?
Higher priority goes to the substituent group with the highest atomic number. If the atoms are the same, continue moving outward until the first point of difference.
What does E mean?
Trans/Opposite sides of the molecule
What does Z mean?
Cis/Same side of the molecule
What is an unsaturation number?
Gives info on number of rings and/or pi bonds.
Why are aklenes & alkynes unsaturated?
They don’t have the max # of hydrones since there is a C-C double or triple bond.
What is the degree of unsaturation?
Each ring and/or pi bond reduces number of hydrogens by 2.
What is the equation to determine unsaturation number?
Why is an alkene more polar than an alkane?
The C-C double bond creates partial negativity.
How does acid strength relate to bond order?
single bond < double bond < triple bond
Why are trans alkenes more stable?
They lack Van der Waal repulsions.
How does the number of alkyl substituents at the double bond affect the stability of an alkene?
More substituents on the alkene carbon = more stable (hydrogens do not count)
Why is the more substituted alkene more stable?
Due to hyperconjugation which is when there molecules in the same plane that can overlap their electron clouds that strengths the p orbital.
What is Markovnikov’s rule?
During an addition of an alkyl halide, the Halogen will always go on the carbon with more substituents (excluding H). The H will always go on the carbon with more H.
What are the 2 steps in the mechanism of addition of hydrogen halides to alkenes?
- High energy pi bond attacks proton
- Carbocations are reactive intermediates that attract halogens.
Which carbocations are more stable?
tertiary > secondary > primary
Why are tertiary carbocations more stable?
More substituents on the Carbon = more ability to hyper-conjugate
What are the types of carbocation rearrangements?
-methyl shift
-hydride shift
How do you know when carbocation rearrangements happen?
- A rearrangement almost always occurs when a more stable carbocation can result.
- The group that migrates in a carbocation rearrangement comes from a carbon directly attached to the electron-deficient, positively charged carbon of the carbocation.
- Hydride migration typically occurs because it gives the more stable carbocation.
What is a cataylst?
A substance that increases the reaction rate without being consumed.
What occurs in a catalytic hydrogenation of alkenes?
Break all double bonds and add H2.
What are aromatic bonds?
Pi bonds in a benzene ring that are less reactive.
What is the “modified Markovnikov’s rule”?
The carbon of the double bond with fewer substituents becomes bonded to the less electronegative group. The carbon with more substituents becomes bonded to the more electronegative group.
Solvents are generally written _____ the arrow.
Under
Reactants & catalysts are written ______ the arrow.
Over
What are vicinal dihalides?
Halides are connected on carbons right next to each other.
The pi bond is electron rich and therefore serves as a ________.
Nucleophile
In a bromonium ion, which carbon has a partial positive charge? Why?
The longer bond between the EN Br and the carbon means it is weaker so the electrons are pulled closer to the Br. There is only a partial positive charge on the more substituted carbon because it is stabilized by hyperconjugation.
Why is a bromonium ion and not a carbocation ion formed?
- Rearrangments are not observed in bromine addition.
- Bromonium ions have more covalent bonds than a carbocation and every atom has an octet.
What kind of alkene addition reaction is this?
Intramolecular reaction
What is an enantiomer?
When the mirror image of the same molecule is noncongruent (non-overlapping).
What is a chiral molecule?
One that has a non-superimposable mirror image.
What is an asymmetric carbon?
A carbon which is bonded to 4 different groups. An asterisk is used to denote asymmetric carbons.
A molecule that contains only one asymmetric carbon is _______ _______.
Always chiral
If 2 molecules are enantiomers, they are also ______.
Chiral
If the molecule has a plane of symmetry, is it chiral?
No
If the molecule has an enantiomer (non-super imposable mirror image), is it chiral?
Yes
If there is only 1 asymmetric carbon, is the molecule chiral?
Yes
What kind of reaction is this?
Ozonolyis reductive workup
What kind of reaction is this?
Ozonolyis oxidative workup
What is a diastereomer?
When some chiral centers change their configuration, but not all of them.
An acid catalyzed reaction follows what kind of Markovnikov addition?
Normal
What happens in an intramolecular reaction?
The straight chain structure will convert into a cyclo/ring structure.
What kind of reaction is this?
Oxymercuration-reduction
What kind of Markovnikov additions occurs in a hydroboration-oxidation reaction?
Anti-Markovnikov
