Organic chemistry flashcards: 50 mechanisms, reactions and rules

All 50 cards

1. 1
   General formula of alkynes
   $\mathrm{C_nH_{2n-2}}$

   Alkynes contain a C≡C triple bond.
2. 2
   Ether functional group
   An oxygen bonded to two carbon groups: R–O–R′

   Example: diethyl ether.
3. 3
   Amide functional group
   A carbonyl bonded to nitrogen: $\mathrm{R{-}CO{-}NR'_2}$

   The simplest form is $\mathrm{R{-}CONH_2}$.
4. 4
   Acid chloride (acyl chloride)
   $\mathrm{R{-}COCl}$: a carbonyl bonded to chlorine
5. 5
   Reactivity of carboxylic acid derivatives (most to least)
   Acid chloride > anhydride > ester > amide

   Toward nucleophilic acyl substitution. Better leaving groups mean more reactive derivatives.
6. 6
   IUPAC suffixes for alcohols, aldehydes and ketones
   -ol, -al and -one

   Ethanol, ethanal, propanone.
7. 7
   Which has naming priority in IUPAC: a carboxylic acid or an alcohol?
   The carboxylic acid; the alcohol becomes a “hydroxy-” prefix
8. 8
   Hybridization and geometry of a carbon with four single bonds
   $sp^3$, tetrahedral, about $109.5^\circ$
9. 9
   Hybridization and geometry of an alkene carbon
   $sp^2$, trigonal planar, about $120^\circ$
10. 10
    Hybridization and geometry of an alkyne carbon
    $sp$, linear, $180^\circ$
11. 11
    Sigma vs pi bonds
    σ: head-on overlap along the bond axis; π: side-by-side overlap of p orbitals

    A double bond is one σ + one π; a triple bond is one σ + two π.
12. 12
    Resonance structures
    Structures with the same atom positions but different electron placement; the real molecule is a hybrid of them
13. 13
    Stereoisomers
    Isomers with the same connectivity but a different 3D arrangement
14. 14
    Enantiomers
    Stereoisomers that are non-superimposable mirror images
15. 15
    Diastereomers
    Stereoisomers that are not mirror images of each other
16. 16
    Meso compound
    A compound with stereocenters that is achiral because of an internal mirror plane

    Example: meso-tartaric acid.
17. 17
    Chiral center (stereocenter)
    Typically a carbon bonded to four different groups
18. 18
    Maximum number of stereoisomers with $n$ stereocenters
    $2^n$

    Fewer when meso compounds are possible.
19. 19
    Cahn–Ingold–Prelog priority rule
    Higher atomic number at the first point of difference gets higher priority
20. 20
    How do you assign R or S?
    Point the lowest-priority group away; if 1 → 2 → 3 runs clockwise it is R, counterclockwise S
21. 21
    Racemic mixture
    A 50:50 mixture of two enantiomers; it is optically inactive
22. 22
    E/Z isomerism in alkenes
    Z: the higher-priority groups are on the same side of the C=C; E: on opposite sides

    It exists because rotation about a C=C bond is restricted.
23. 23
    SN2 mechanism
    One concerted step with backside attack; rate $= k[\text{substrate}][\text{Nu}]$

    Inverts the configuration at the carbon.
24. 24
    Best substrates for SN2
    Methyl > primary > secondary; tertiary substrates don’t react by SN2

    Steric hindrance blocks backside attack.
25. 25
    Solvent that favors SN2
    Polar aprotic, e.g. DMSO, DMF or acetone
26. 26
    SN1 mechanism
    Two steps through a carbocation; rate $= k[\text{substrate}]$

    Gives a mostly racemic product at a stereocenter.
27. 27
    Conditions that favor SN1
    Tertiary or resonance-stabilized substrates, weak nucleophiles, polar protic solvents
28. 28
    E2 mechanism
    One concerted step with a strong base; H and the leaving group must be anti-periplanar; rate $= k[\text{substrate}][\text{base}]$
29. 29
    E1 mechanism
    Two steps through a carbocation, favored by weak bases and heat; rate $= k[\text{substrate}]$
30. 30
    Zaitsev’s rule
    Eliminations usually give the more substituted, more stable alkene

    Bulky bases such as tert-butoxide favor the less substituted (Hofmann) product.
31. 31
    Carbocation stability order
    Tertiary > secondary > primary > methyl

    Hyperconjugation and inductive effects; allylic and benzylic cations are also stabilized by resonance.
32. 32
    Carbocation rearrangement
    A 1,2-hydride or alkyl shift that turns a carbocation into a more stable one
33. 33
    Product of HBr + propene (no peroxides)
    2-Bromopropane (Markovnikov)

    H adds to the carbon with more hydrogens; Br ends up on the more substituted carbon.
34. 34
    Product of HBr + propene with peroxides
    1-Bromopropane (anti-Markovnikov)

    A radical mechanism puts Br on the less substituted carbon.
35. 35
    Hydroboration–oxidation of an alkene
    Anti-Markovnikov alcohol with syn addition ($\mathrm{BH_3}$; then $\mathrm{H_2O_2}$, $\mathrm{NaOH}$)

    No carbocation, so no rearrangements.
36. 36
    Acid-catalyzed hydration of an alkene
    Markovnikov alcohol ($\mathrm{H_2O}$, $\mathrm{H_2SO_4}$), through a carbocation

    Rearrangements are possible.
37. 37
    What makes an organic acid stronger?
    A more stable conjugate base: negative charge spread by resonance or held by electronegative atoms
38. 38
    Typical $\mathrm{p}K_a$ of a carboxylic acid, a phenol and an alcohol
    About $4\text{–}5$, $10$ and $16\text{–}18$
39. 39
    Hückel’s rule
    A cyclic, planar, fully conjugated ring is aromatic with $4n + 2$ π electrons

    Benzene has 6 π electrons (n = 1).
40. 40
    Electrophilic aromatic substitution
    An electrophile replaces a hydrogen on an aromatic ring through a sigma complex (arenium ion), keeping the ring aromatic
41. 41
    Ortho/para-directing groups
    Activating groups such as $\mathrm{-OH}$, $\mathrm{-NH_2}$, $\mathrm{-OCH_3}$ and alkyls, plus the halogens

    Halogens deactivate the ring but still direct ortho/para.
42. 42
    Meta-directing groups
    Strongly deactivating groups: $\mathrm{-NO_2}$, $\mathrm{-CN}$, $\mathrm{-SO_3H}$, $\mathrm{-CF_3}$ and carbonyl groups
43. 43
    Reagents for nitrating benzene
    $\mathrm{HNO_3}$ with $\mathrm{H_2SO_4}$, which generate the nitronium ion $\mathrm{NO_2^+}$
44. 44
    Nucleophilic addition to a carbonyl
    A nucleophile attacks the electrophilic carbonyl carbon, forming a tetrahedral intermediate
45. 45
    Grignard reagent + ketone, then aqueous workup
    A tertiary alcohol

    With an aldehyde: a secondary alcohol; with formaldehyde: a primary alcohol.
46. 46
    $\mathrm{NaBH_4}$ vs $\mathrm{LiAlH_4}$
    Both reduce aldehydes and ketones to alcohols; only $\mathrm{LiAlH_4}$ also reduces esters and carboxylic acids (to primary alcohols)
47. 47
    PCC oxidation of a primary alcohol
    An aldehyde (PCC stops there)

    Stronger oxidants such as chromic acid or KMnO₄ go on to the carboxylic acid; secondary alcohols give ketones.
48. 48
    Fischer esterification
    Carboxylic acid + alcohol $\rightleftharpoons$ ester + water, with an acid catalyst

    It is an equilibrium; excess alcohol or removing water drives it forward.
49. 49
    Aldol reaction
    An enolate adds to another aldehyde or ketone, giving a β-hydroxy carbonyl compound

    Losing water (aldol condensation) gives an α,β-unsaturated carbonyl.
50. 50
    Diels–Alder reaction
    A [4+2] cycloaddition of a conjugated diene with a dienophile, forming a cyclohexene ring

    The diene must adopt the s-cis conformation; the reaction is concerted.