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ACS ORGANIC CHEMISTRY FINAL EXAM
2025 /2026 QUESTIONS AND ANSWERS
What will adding CHBr3 and KOH to an alkene do?
What is the formula used to determine number of stereoisomers in a compound?
2^n
How to determine stereogenic centers in a molecule?
Whenever a compound is bound to 4 different groups! PLEASE don't forget to check every group!
Which kinds of diols can HIO4 cleave? What does it form?
-It only cleaves 1/2 diols that are cis with respect to each other -It forms either an aldehyde or a ketone
How can you create a carboxylic acid from an alkene?
Use KMnO4, acid, and heat; This will cleave the double bond; an aldehyde will be reduced to a carboxylic acid; a secondary double bond will form a ketone -Ozonolozysis will cleave it until the aldehyde; KMno4 will cleave it until the carboxylic acid
Tertiary alcohols are highly resistant to what?
Oxidation
What happens when you take a ketone and you react it with H2 gas and Raney Nickel?
An alcohol will be formed
What does NaNH2 do with a terminal alkyne?
What does H2 and Pd/C reduce?
It reduces a C=C faster than a C=O bond; adds two Hs across the double bond
What only reduces a C=O bond but not a C=C bond?
NaBH4 and LAH
Are combustion rxns endo or exo?
Exothermic
What is the IHD (index of hydrogen deficiency?
IHD = 2n+2-H all divided by 2; if N decrease number of H by 1; if halogen increase number of H by 1; make no changes for O
What is hydrogenation?
Add H2 and Pd/C; add H
Functional group: alkane
Functional group: alkene
Functional group: alkyne
Functional group: benzene ring (phenyl)
Functional group: amine
Functional group: alcohol
Functional group: ester
Functional group: carboxylic acid
Functional group: amide
When naming organic molecules, what are the two basic rules?
- Identify the longest chain
- Give substituents the lower number
Stability of carbocations
-the primary allylic carbocation is more stable than secondary carbocation and less stable than tertiary carbocation -the secondary allylic carbocation is less stable than the tertiary carbocation (unsure about this one; online it says that secondary allylic is more stable than a normal tertiary carbocation; have to do experiments to determine this) -tertiary allylic carbocation is more stable than a tertiary carbocation
Why is a tertiary carbocation more stable than a secondary carbocation?
Due to the inductive effect and hyperconjugation
What is hyperconjugation?
spreading out charge by the overlap of an empty p orbital with an adjacent sigma bond
Why is a primary allylic carbocation more stable than a secondary carbocation?
Due to resonance
No, because it violates the octet rule
How to determine strongest acid or most acidic compound in a molecule?
*Always look at stability of the conjugate base to determine acid strength -ERIH (or HIRE): E - element effects R - resonance I - inductive effect H - hybridization
As the pKa decreases, the strength of the acid...
increases
Write the pKa values of the structures Dr. Aguilar asked us to memorize
What is the approximate pKa of a sulfonic acid? Why is sulfonic acid more acidic than carboxylic acid?
-2, negative charge can be distributed among three oxygen atoms
How does acidity increase in the periodic table?
It increases from left to right due to increasing electronegativity and from top to bottom due to increasing size: HI would be strongest acid
When naming alkenes, what should be taken into consideration?
-Give the double bond the highest prioirty when numbering -largest priority groups on opposite sides of the double bond should be taken into consideration when determining E or Z stereoisomers
When determining R/S configuration, what should be taken into consdieration?
-The lowest priority group (usually H) must be in the back
What are the steps do determine R/S configurations using the method by Ochem tutor?
-Identify 4 groups that you have -Put group in the back in a circle (or in front but switch it after) and put groups above and relative to it around the group in the circle -rotate the molecule to get 4 on top -flip the molecule so 4 comes down to the center -determine R/S; switch if you initially had it in the front
What do you get when you combine an alkene with OsO4 and H2O
Syn dihydroxylation
Why are sp hydrogens more acidic than sp2 or sp3?
Sp carbons have more s-character, so they will stablize the negative charge better (there is increased electronegativity)
Vinylic or aryl halides do not react in which reactions?
SN2/SN
Will a primary allylic alkyl halide or primary alkyl react more rapidly in an SN reaction?
The primary allylic halide; it's more reactive in both SN1 and SN2 situations
Describe the SN2 reaction
The nucleophile attacks the carbon compound from behind, ejecting a leaving group of the compound. -reacts best with methyl and primary alkyl halides and sometimes with secondary if it is in a polar aprotic solvent -inversion of stereochemistry
- methyl, primary, and secondary alkyl halides
- high concentration of Nu
- strong nucleophile
- polar aprotic solvent
- moderate temperature (25 degrees Celsius)
What is a polar aprotic solvent and what reaction does it favor?
-do not have any OH or NH groups -SN2 reactions
Describe the SN1 reaction
-formation of carbocation before nucleophilic attack -reacts best with tertiary alkyl halides and sometimes secondary alkyl halides if in polar protic solvent -racemic mixture since nucleophile can attack from the front and the back
- tertiary and secondary only if in a polar protic solvent
- low concentration of Nu
- weak Nu (such as H2O or -OAc)
- polar protic solvent is best
- moderate temperature (25 degrees Celsius)
Hydrohalogenation of alkene; what is important about this mechanism? What reagents are needed?
Carbocation rearrangements are possible (hydride and methyl shifts); Markovnikov rule applies -halogen is needed; HBr, HCl, HI (possibly) -syn/anti addition possible
-reagents: X2 (Br2, Cl2, etc) and H2O -anti addition due to backside attack of water; attack the more substituted side because it is the most electrophilic
What is another way to form a halohydrin? (reagents)
NBS and DMSO and H2O; will give you Br and OH halohydrin; OH goes to more substituted side
Hydroboration-oxidation; mechanism and reagents
-reagents: BH3 and H2O2, HO- -mechanism: form an alkylborane first (H and BH2 added to the double bond), then water added to the double bond -syn addition -BH2 bonds to least substituted side
Reaction of an epoxide with a strong nucleophile and water
-backside attack at least substituted side; SN2 reaction
Reaction of an epoxide with an acid (HBr)
-protonate the O first, then attack with remaining nucleophile at more substituted side (turns out the more substituted side is more electrophilic) -SN2 reaction; backside attack
What do the reagents Hg(OAc)2, H2O followed by NaBH4 do?
They create the Hgionium ion, then water attacks the more substituted side b/c it's more electrophilic, then HgOAc is substituted by H
Describe initiation step for radical reactions?
Form radicals; radicals at end of rxn
What is essential in a radical reaction? (3 things)
-heat -light -radical initiators (RO-OR, AIBN)
What are the three reactions of radicals?
Describe chlorination and bromination with hv
-Cl2 forms an equal mixutre; reaction is fast (exothermic; TS most closely resembles the reactant) -Br2 only forms the product where Br is on the more substituted side due to formation of a radical; reaction is slow (endothermic rxn, TS most closely resembles the product - Hammond's postulate)
What is the stability of radicals?
The primary allylic radical is the most stable because it is resonance-stabilized
Describe selective bromination at allylic C-H bonds. What reagents are needed? What is important about this reaction?
NBS, (hv, heat, or ROOR, AIBN) -IT IS SELECTIVE FOR ALLYLIC C-H BONDS
Determine the mechanism of butene with NBS, hv or ROOR
What are the two ways that HBr can be added to an alkene?
-Markovnikov (HBr only) and anti-Markovnikov (HBr and hv, light, or peroxide)
