The # of MO's = _______
# of AO's
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| Term | Definition |
|---|---|
The # of MO's = _______ | # of AO's |
What 2 ways can AO's combine to give MO's? | Additive and Subtractive |
What is additive combination?
3 | - Leads to bonding MO's
- Lower in energy than AO's
- electrons sharing space |
What is subtractive combination?
3 | - Leads to antibonding MO's
- Higher in energy than AO's
- Electrons are not in shared space |
In an alkene, ___ p orbitals overlap in side-to-side fashion to make ___ pi MO's | Two
Two
- gives one bonding and antibonding orbital |
What do you classify the bonding MO to be? | HOMO |
What do you classify the antibonding MO to be? | LUMO |
How many MO's does the allyl cation have? | 3 p orbitals, 3 C atoms, 3 pi MO's (bonding, nonbonding, antibonding) |
How many nodes exits in an allyl cation MO diagram? | O->2 |
T/F: the lowest energy MO will never have a node | True |
In a conjugated diene, how many MO's are there | 4 p orbitals, 4 C atoms, 4 pi MO's (2 bonding, 2 antibonding) |
How many nodes exist is conjugated diene MO's? | 0->3 |
The greater the conjugation, the _____ energy of MO's | Lower |
Electronic configuration of a diene is ____ in energy than an alkene | Lower |
T/F: Isolated DB are more stable than conjugated DB | False |
Describe isolated DB | Multiple bonds separated by one or more saturated (single bond) C atoms |
Describe cumulated DB | Two or more DB connected by common C atom
- Internal C is sp-hybridizied |
Describe conjugated DB | Connected p orbitals
- Delocalization of pi e-
- One atom w/ p orbital next to at least on pi bond
(Atom can be heteroatom, carbanion, radical, DB/TB) |
You should push arrows from __________
3 | - Neg charge
- LP
- Pi bond |
If there is no _________ , you cannot draw resonance structures | Conjugation |
More ________ bonds = More stable | Covalent |
Complete valence shell around each atom = ____ stable | More |
Charges are close together = _____ stable | More |
What is the abs maxima of most isolated alkenes? | Below 200 nm |
What is the abx maxima of most conjugated alkenes? | Above 200 nm |
What are absorbances a result of? | E- excitation from HOMO to LUMO |
The smaller the HOMO-LUMO gap, the _______ energy needed for excitation | Less |
The HOMO-LUMO gap gets _______ as conjugation increases | Smaller |
Less energy means what for wavelengths? | Longer |
What are the 2 types of electrophilic additions 1,3-dienes can undergo? | - 1,2 addn of HX to 2 C's of a DB
- 1,4 addn of HX to 2 terminal (end) C's of conjugated system |
Which is the kinetic and thermodynamic product?
| Kinetic: 1,2 Product
Thermodynamic: 1,4 Product |
At low temps, there is not enough energy to reach highest TS, so the FASTEST product is_____ | 1,2 Kinetic |
Is the formation of the kinetic product reversible or irreversible? Why? | Irreversible
- Not enough energy to go back to allyl cation |
At high temps, there is enough energy to achieve higher TS, so the MOST STABLE product is______ | 1,4 Thermodynamic product |
T/F: The most stable (lowest energy) alkene will have least subbed DB | False, it will have most stable DB |
Is the formation of the thermodynamic product reversible or irreversible? Why? | Reversible
- There is enough energy to go back to allyl cation |
What is a pericyclic rxn? | Rxn where movement of e- flows through ring-like TS, can only proceed if phases of MO's are matched |
What is a diene and dienophile? Whats e- poor/rich? | Diene: 4 pi e- (e- rich/nucleophile)
Dienophile: 2 pi e- (e- poor/electrophile) |
What conformation must the diene adopt? Why? | Cis (to bring 2 terminal C in close proximity to dienophile) |
The closer the HOMO-LUMO orbitals are in energy, the _______the rate of rxn | Faster |
EDG on the diene will _____ energy of HOMO | Raise |
EWG on dienophile will ______ energy of LUMO | Lower |
If either the diene or dienophile is _______, the product of diels alder will only have one product | Symmetrical |
If either the diene or dienophile is ______, the product of diels alder could have 2 diff products | Asymmetrical |
Placement of EDG on diene and EWG dienophile on can control what? | Regioselectivity |
If the dienophile is cis, what will the product be? | Cis |
Describe what an EXO product is | Dienophile approaches diene when EWG is outside and away from diene |
Describe what an ENDO product is | Dienophile approaches diene when EWG is inside and towards diene |
Which approach is favoured: endo or exo? Why? | Endo
- Stacking pi orbitals and stabilizing interactions of the pi systems |
How do you get a racemic mixture of products in the diels alder rxn? Why? | - Endo approach of dienophile can occur from bottom or top of diene |
What is a racemic mixture? | Contains equal amounts of two enantiomers |