Exam 2 Flashcards
complexation reaction
making a new sigma bond
decomplexation reaction
breaking a sigma bond
substitution reaction
sigma bond broken and replaced
addition reaction
breaking a pi bond and forming two new sigma bonds
elimination reactions
forming a pi bond and breaking two sigma bonds
dehydrobromination
dehydration
dehydrogenation
ΔG‡
activation energy
- fast or slow reaction?
- distance from ground state energy to transition state
- higher ΔG‡, few molecules can react/overcome barrier/requirements –> slower reaction
ΔG°
Standard free energy
- favorable or unfavorable?
- ΔG°: products are more stable than reactants (Keq > 1)
ΔG° = 0: products and reactants energies are equal; Keq = 1; reaction at equilibrium
+ΔG°: products less stable than reactants; Keq < 1; reverse reaction is favored
transition state
highest energy point between steps on an energy diagram
rate determining step
highest “hill” on rxn coordinate; height determines the reaction speed –> higher hill, slower reaction
pKa and reaction stability
Higher pKa –> weaker acid –> more stable bond –> lower energy –> harder to break
thermodynamic control
- if all steps are reversible; relative stability dictates the outcome
- thermodynamic product: more stable/lower energy product favored and formed when system reaches equilibrium
kinetic control
- irreversible reactions: when the reaction doesn’t “know” which path leads to the most stable product
- kinetic product: formed faster because it requires less energy, even if less stable (higher energy)
what do you consider for stability of a molecule
- aromaticity
- resonance contributors
- delocalization
aromaticity
- aromatic compounds more stable and lower energy
- criteria for aromaticity: must be closed ring structure (cyclic), every atom in the ring must have a p-orbital (no sp3 atoms), molecule must be planar/flat, number of delocalizable pi electrons in 4n + 2 equation is even and NOT multiple of 4
antiaromaticity
- high energy: antiaromatic compounds are high energy and very unstable
- criteria: satisfies all the criteria for aromaticity, except the number of deocalizable pi electrons in 4n + 2 equation is a multiple of 4
- slow and difficult reaction due to high energy and instability
nonaromaticity
- energy level: between aromatic and antiaromatic compounds; typically more energetically favorable and stable
- nonplanar
- faster and easier reactions because more energetically favorable
disruption of aromaticity
makes the reaction thermodynamically unfavorable
inductive effect
EN atoms without resonance involvement destabilize carbocations due to the inductive effect
weak acids
pKa 5-18 need a catalyst for EAR
EAR steps
- any acid base chemistry
- protonate alkene with strongest acid around
- form carbocation (rate of protonation faster is carbocation intermediate is more stable
- carbocation capture: CC is quickly captured by the original weak acid (acting as a Lewis base) ,forming a cationic intermediate
- deprotonation: cationic intermediate is deprotonated, yielding final product
major/minor products for EAR
- more substituted carbocation (more carbons attached) is more stable
- resonance stabilization (resonance trumps substitution in determining stability)
carbocation stability
- resonance stability and delocalization trumps degree of substitution
- degree of substitution: 1 degree (bonded to one other carbon), and so on
- hyperconjugation: good consideration when only degree of sub of a CC is the difference being compared; more sp3 alkyl groups = more electrons available for hyperconjugation = more stable carbocation; bonding orbital donates electron density to empty p orbital of the carbocation, stabilizing it
regioisomers
structural isomers that differ in position of their functional groups
- major regioisomer: protonation occurs on less substituted end of the double bond
markovnikov’s rule
- predicts regioselectivity
- the H atom from the reagent adds to the end of the C=C bond with MORE H ATOMS
- regioisomer formation: two possible regioisomers and choose major/minor product
HNMR integration
size/height of the signal
- each signal height represents the number of H atoms in each equivalent group
- taller signals –> more equivalent Hs
molecular symmetry
super symmetrical molecules = fewer NMR signals
chemical shift
position of signals on horizontal axis
- Left (downfield, high δ) = High chemical shift; Closer to an electronegative (EN) atom; Higher deshielding (less electron density around the atom)
- Right (upfield, low δ) = Low chemical shift; Further from an EN atom, more shielded
