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OChem Midterm
midterm1
| Question | Answer |
|---|---|
| Branched or unbranched hydrocarbons have higher boiling point? | Unbranched |
| What can you use to determine most acidic proton? | Electronegativity, and resonance |
| A hydrogen on the alpha position of a carbonyl is _____ acidic | weakly |
| In radical addition, what wont you see? | CH3 and Br on same cyclo carbon |
| ROOR is a tipoff that? | It's a radical |
| ROOR does not work with H - ____ | Cl |
| Alkanes show __ chemical affinity for other substances | little |
| Are alkanes often involved in chemistry of living organisms? | NO |
| During combustion, what are the products? | carbon dioxide, water |
| Does RXN of alkane with Cl2 occur? | Yes, when the mixture is irradiated with UV light |
| A standard Newman projection represents how many carbons? | 2 |
| What causes the free rotation around the C-C bonds in ethane? | the sigma bond |
| gauche conformation causes what sort of strain? | steric |
| In methylcyclohexane, which conformation is more stable: the equatorial or axial? | equatorial |
| what is the cause of the steric strain on axial conformations of substituted cyclohexanes? | the axial methyl group on C1 is too close to the axial hydrogens 3 carbons away. |
| on an axial monosub'd cyclohexane, how many axial interactions with hydrogens would the substituent have? | 2; an axial interaction with the hydrogen on either side |
| in disubstituted cyclohexanes, is the equatorial position always more stable | no, need to analyze all steric interactions in the possible chair conformations before deciding which is favored |
| what is the common structure of steroids? | 3 six membered rings, 1 five membered ring fused together |
| which cycloalkane is strain-free? | cyclohexane, b/c it adopts puckered chair conformation |
| Which type of radicals do NOT form? | Phenyl |
| how do you determine stability of a carbocation? | stability increases from primary to tertiary |
| what is the hydration reaction? | water adds to alkenes to yield alcohols |
| in these acidic reactions, what do you look for? | the spot with most carbons attached |
| what is the first step with acidic hydration and alkene/ring? | it degrades the alkene to an alkane |
| whats second step with acidic hydration? | H2O comes to the rescue |
| in radical RXNS, what can be a terminating step? | when 2 radicals come together to form a stable product |
| in radical substitution: which is selective: chlorine or bromine? | bromine |
| in radical substitution: which position types WONT chlorine go after? | phenylic and vinylic |
| are metals more or less EN charged than a carbon? | less |
| if Keq is less than 1 ... | the RXN goes in the reverse direction, from right to left |
| what is Gibbs free energy change? | the E change that occurs during a chemical RXN |
| does Keq tell you the rate of RXN or how fast equilibrium is reached? | NO |
| how can you tell if radical substitution? | hv, single blonds, Cl/Br |
| how can you tell if radical addition? | ROOR, HBr, double bond |
| how can you tell if electrophilic addition? | no hv, no ROOR |
| if you break pi, sigma, sigma and have sigma, sigma sigma, exo/endothermic? | exothermic |
| when asked about acid/base stability, consider: | the 4/5 rules, and whether tertiary, primary, etc. |
| whats the mnemonic for electrophilic addition? | most, basic, rescue. you add HBr across the double bond |
| when delta G is positive, Keq is ... | negative |
| when delta G is negative, which side preferred? | right side |
| what is the gauche value between CH3 and Br on Newman projection? | 0.3 |
| What is the gauche value between Ch3 and CH3 on Newman projection? | 0.9 |
| when you think of thermodynamic stability, think.... | internal double bonds more stable than external, and, the more carbons on it, the more stable. |
| if multiple carbocations could form...which one do you choose? | the more stable one, based on the ranking 3>2>1.. |
| why is it that usually the first carbocation intermediate is a slow transition? | because it does not obey octet rule |
| break weak bonds, form strong bonds: ____thermic | exothermic |
| when determining sign of enthalpy, entropy, gibbs free energy: | delta H: use what type of bonds broken/formed delta S: use randomness delta G: use equation |
| how many transition states in electrophilic addition? | 2 |
| what is "bromination"? | electrophilic addition with Br2 |
| in one line, what happens with electrophilic addition? | you add ___ across the double bond |
| which electrons are relatively open to attack? | pi electrons in a pi orbital |
| Name a superbase: | LiCH3 |
| Name some polar protic molecules: | H2O, D2O |
| another last way to evaluate side preferred: | can tell which is stronger acid/base by, which one more likely to donate protons..etc. |
| recap: how to tell which side preferred? | stability rules, stronger acid/base, the trend |
| least acidic protons are : | methylic |
| protic conatin which bonds? | O-H or N-H |
| all transition metal cations are Lewis ___ | acids. Al, B, Magnesium ion |
| when forming a standard carbocation, the formal charge will want to reside on the | most alkyl substituted side. (b/c more stable) |
| the energy profile goes down..due to: | progressive obeying of octet rule |
| what is LDA? | N with two isopropyls attached |
| Name 2 basic nucleophiles: | NaOH, LiNH2 |
| Name 2 acidic non-nucleophiles: | H2SO4, H3PO4 |
| CH3MgBr is a ___ | Superbase! |
| a strong acid has a stable ___ | conjugate base |
| external double bonds: more or less stable than internal? | less stable (more unstable) |
| greater alkyl substitution, the __ stable the double bond | more stable |
| all transition metal cations are: | Lewis acids |
| what does LDA do? | dehydrohalogenates |
| what else dehydrohalogenates? | NaNH2 with acetone |
Created by:
kay21
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