Organic II - Conjugation Systems (Chp 15) Flashcards
When does conjugation occur?
Whenever p orbitals can overlap on 3 or more adjacent atoms.
Conjugated double bonds are separated by a _________ bond.
single
Isolated double bonds are separated by ________________ bonds.
2 or more single
Conjugated double bonds are _____ stable than other bonds.
more
Conjugated double bonds have extra ______.
stability
The more stable the compound, the less heat released during _____________.
hydrogenation
How many lobes does each p orbital have with the wave function?
2 lobes
How many p orbitals does 1,2-dibutene have?
4 p orbitals (atomic orbitals)
When lobes overlap constructively, what is formed?
A pi bonding (p) MO is formed
Even number of MOs leads to an…
even number of bonding and antibonding MOs.
The number of atomic orbitals equals…
the number of molecular orbitals (MO).
Odd number of MOs means there are…
bonding, antibonding and a bonding MO.
The maximum number of nodes equals…
n-1 (n = number of atomic orbitals)
What creates nodes?
Antibonding
Which is more stable, s-trans or s-cis? Why?
s-trans b/c it has no interference b/w protons.
Describe an allylic carbon.
The carbon directly attached to an sp2 carbon (double bonded carbon).
Which is more stable? s-trans or s-cis?
s-trans
Molecules with resonance structures are more ______ than those that don’t.
stable
List the order of stability for carbocations.
CH3+ < primary < secondary, primary allylic < tertiary, secondary allylic
Which forms faster? Kinetic product or the thermodynamic product?
Kinetic product.
List the radical stabilities.
1 < 2 < 3 < 1 allylic
NBS provides a low, _________ concentration of ___.
constant; Br2
NBS reacting with HBr by-product to produce Br2 to prevent what?
HBr addition across the double bond.
Are there any bonding interactions when there are only nodes?
No.
Diel-Alder reactions produces a ____.
ring
How many steps does diels-alder reactions take?
One.
What two reactants are needed in Diel-Alder reactions?
A diene and a dienophile.
The diene in Diels-Alder reactions need to be in ___ conformation.
cis
Dienes like to react with an ____________ alkene to give cyclohexene or cyclohexadiene rings.
electron-poor
Why is a 1,3-cyclopentadiene more stable than 2,3-butadiene?
Because the double bonds are fixed in the cyclic compound and is in cis conformation.
For Diels-Alder rxc, diene must be in ____ conformation.
s-cis
For Diel-alder reactions, what of kind of products will you always get?
1,2- and 1,4-product
What are the steps to finding a diene and dienophile? (3 steps)
1) Find the 6 C ring with double bond
2) Draw the 3 arrows starting from the pi bond
3) Draw the diene and dienophile
What does pericyclic reaction mean?
Everything happens in one step.
What is an example of a pericyclic reaction?
Diels-Alder reaction
MOs must overlap ____________ to stabilize the ____________ state in pericyclic reactions.
constructively; transition
An energy gap in ultraviolet spectroscopy is _______ with conjugated dienes than other dienes.
higher
The lower the energy, the ________ the wavelength.
longer
What does the spectrometer measure?
The intensity of a reference beam through solvent only (Ir) and the intensity of a beam through a solution of the sample (Is)
What law does absorbance follow?
Beer’s Law
Give the formula for absorbance.
A = εcl
ε - molar absorptivity
c - sampel concentration in moles per liters
l - length of light path in cm
The more conjugation, the ________ the wavelength, and the ________ the gap between MOs.
longer; smaller
To see if a reaction is photochemically produced what must happen?
The HOMO+ of diene and LUMO of dienophile must be bonded on both sides.
