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34 Cards in this Set
- Front
- Back
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conjugated
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alternating single and double bonds; single bonds can rotate around double bond
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conjugated properties
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shorter single bond (6 pm shorter = 147 pm)
and especially stable |
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What is the relationship between stability and substituants
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more highly substituted release less heat, contain less energy to start with. makes them more stable. This is proven by heat of hydrogenation. There will be less energy difference than what is expected, this is called resonance energy. single bond heat of hydrogenation is 126.
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Heat of hydration of one double bond is 126. So what would be the resonance energy of CH=CH-CH=CH
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EXPECTED (126X2)= 252 but actually 236. resonance energy of 16 kj less than expected.
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What accounts for stability of conugated dienes?
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orbital hybridization. in typical C-C bonding there is sigma overlap of sp3 orbitals. In conjugated dienes there is sigma overlap of Sp2 orbitals. Molecular orbital increases in level with increasing nodes
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three types of dienes
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(1) isolated/nonconjugated: isolated double bonds from each other (2) conjugated: separated by one single bond, resonance forms (3) double bonds directly connected
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Stability rules of dienes
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(1) conjugated most stable (2) trans is more stable than cis
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Properties of Benzene
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(1) 150 kj/mol less negative than we might expect (2) bond angle of 120 (3) sp2 hybridized (4) carbon carbon bond length of 139 - intermediate etween 154 single and 134 double
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Huckels rule
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aromatic 4n+2
nonaromatic 4n |
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Why is Huckels rule true?
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when electrons fill various molecular orbitals, it takes two electrons to fill the lowest lying orbital and four electrons for each n suceeding energy levels
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What does HOMO and LUMO
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Highest occupied MO
lowest occupied MO |
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The greater the extent of conjugation....
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the less energy needed, the longer the wavelength
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conjugation will show between what UV range
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200-400
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heterocycle
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cyclic compound that contains atoms of two or more elements in its ring, usually carbon along with nitrogen, oxygen or sulfur
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As conjugation increases what occurs between HOMO and LUMO
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the difference decreases with increasing conjugation
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dienophyle
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electron withdrawing
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stereospecific
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a single product stereo isomer is formed
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exo/endo
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endo - down to bridge (anti-syn)
exo - syn to bridge |
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C-H occurs at what H NMR
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3030
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out of plane bending can be used determine substitution pattern on an aromatic ring at what H NMR
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690-900
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aromatic carbons absorb in the range
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110-140
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Diels aldter only form ____ because overlap and substituent on dienophile is underneath diene
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endo
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requirements for Diene alders rxn
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(1) Diene must be in cis (2) substituents effect rate, more sibstituents faster (3) DA used to form bicycic systems
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To follow huckels rule must be
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planar, continuous, monocyclic array of p type orbitals
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Problems with Friedel craft
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(1) no vinyl or aryl halides are reactive for X-R (2) substituted aromatics non reactive with carbony or amino group (3) sometimes get skeletal rearrangement (4) must be at least as reactive as chlorobenzene as substituent
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Inductive withdrawal groups
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halogens, hydroxyl groups, cyano, nitro, carbonyl
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inductive Withdrawing (-I) groups
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alkyl groups; decrease electron density less reactive
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inductive donating (+I)
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alkyl group
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The less reactive you _____ electron density
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decrease
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Resonance withdrawing groups (-R)
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pi bond or triple bond; carbonyl cyano nitrile; leave positive charge
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Resonance donating groups (+R)
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halogen, hydroxyl (OH), alkoxyl (OR); leave negative charge
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At what side is the most reactive interaction between resonance and inductive effect
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+I, +R
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Reactivity _____ with electronegative increase
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decreases
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What is the definition of activating and deactivating groups in comparison to benzene
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activating more reactive than benzene, deactivating is less reactive
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