General Organic Chemistry flash cards

1. 1.What is the inductive effect?

   The permanent displacement of $\sigma$ (sigma) bond electrons along a chain of atoms due to an electronegativity difference. It is a permanent effect, transmitted through sigma bonds, and its magnitude decreases rapidly with distance (nearly negligible after 3 carbons).

   Hint: Sigma electrons, electronegativity difference.

2. 2.Distinguish between the $-I$ (electron-withdrawing) and $+I$ (electron-releasing) inductive effects.

   A $-I$ group pulls sigma electrons toward itself (e.g. $-NO_2$, $-CN$, $-COOH$, halogens); a $+I$ group pushes electron density away from itself (e.g. alkyl groups like $-CH_3$, and $-COO^-$, $-O^-$). Reference standard is the $C-H$ bond (taken as zero).

   Hint: Withdrawing vs donating; H is the zero reference.

3. 3.Arrange the following in order of increasing $-I$ effect: $-NH_2$, $-OR$, $-F$, $-NO_2$.

   $-NH_2 < -OR < -F < -NO_2$. In general the $-I$ order runs roughly: $-NR_3^+ > -NO_2 > -CN > -COOH > -F > -Cl > -Br > -I > -OR > -NH_2$.

   Hint: More electronegative / positively charged = stronger.

4. 4.What is resonance (mesomerism)?

   When a single Lewis structure cannot describe a molecule fully, the real structure is a resonance hybrid of two or more contributing (canonical) structures that differ only in the position of electrons (not nuclei). The hybrid is more stable than any single canonical form; this extra stability is resonance energy.

   Hint: Delocalized electrons, hybrid of canonical forms.

5. 5.State the essential conditions for resonance.

   (1) Atoms sharing the delocalized electrons must be roughly coplanar; (2) there must be conjugation — alternate single and multiple bonds, or a lone pair / empty orbital / radical adjacent to a multiple bond; (3) canonical structures differ only in electron positions, keeping the same relative arrangement of atoms.

   Hint: Coplanarity + conjugation + only electrons move.

6. 6.What features make a resonance (canonical) structure more stable / a larger contributor?

   More stable canonical forms have: (1) more covalent bonds, (2) all atoms with complete octets, (3) least separation of unlike charges, (4) negative charge on the more electronegative atom and positive charge on the more electropositive atom.

   Hint: More bonds, complete octets, minimal charge separation.

7. 7.Distinguish the mesomeric effect ($M$ or $R$) from the inductive effect.

   The mesomeric (resonance) effect involves delocalization of $\pi$ (pi) electrons or lone pairs through conjugation and is transmitted without loss over the whole conjugated system. Inductive effect involves $\sigma$ electrons and dies out rapidly with distance.

   Hint: Pi/lone-pair delocalization vs sigma polarization.

8. 8.Distinguish $+M$ (electron-donating by resonance) from $-M$ (electron-withdrawing by resonance) groups.

   $+M$ groups donate a lone pair into the conjugated system (e.g. $-OH$, $-OR$, $-NH_2$, $-Cl$, $-Br$). $-M$ groups withdraw pi electron density into themselves (e.g. $-NO_2$, $-CN$, $-CHO$, $-COOH$, $-COR$).

   Hint: Lone-pair donors vs pi acceptors.

9. 9.What is hyperconjugation?

   Delocalization of the electrons of a $\sigma$ (C–H) bond adjacent to an unsaturated system (double bond, carbocation, or radical) into the empty or partially filled p-orbital / pi system. Also called the no-bond resonance or Baker–Nathan effect.

   Hint: Sigma C–H electrons overlap with adjacent p/pi orbital.

10. 10.How does the number of $\alpha$-hydrogens relate to hyperconjugative stabilization?

    Stabilization increases with the number of $\alpha$-hydrogens (C–H bonds on carbon adjacent to the double bond / positive centre / radical). More $\alpha$-H means more hyperconjugative structures and greater stability.

    Hint: More alpha C–H bonds = more no-bond structures.

11. 11.What is the electromeric effect ($E$)?

    A temporary, complete transfer of a shared pair of pi electrons to one of the bonded atoms, occurring only in the presence of an attacking reagent. It disappears when the reagent is removed. $+E$: pi pair moves toward the attacking reagent; $-E$: pi pair moves away.

    Hint: Temporary pi shift, only when a reagent attacks.

12. 12.Contrast the electromeric and mesomeric effects.

    Electromeric effect is temporary and requires an attacking reagent (complete transfer of the pi pair). Mesomeric (resonance) effect is permanent and exists in the ground state without any reagent (partial delocalization).

    Hint: Temporary + reagent-driven vs permanent + inherent.

13. 13.Define a reaction intermediate. Name the three common carbon intermediates.

    A short-lived, reactive species formed transiently during a multi-step reaction. The three common carbon intermediates are the carbocation (positive carbon), carbanion (negative carbon), and free radical (unpaired electron on carbon).

    Hint: Carbocation, carbanion, free radical.

14. 14.Describe the structure of a carbocation.

    A carbon bearing a positive charge with only six valence electrons. It is $sp^2$ hybridized, planar/trigonal, with an empty unhybridized p-orbital. It is an electron-deficient electrophile.

    Hint: $sp^2$, planar, empty p-orbital, 6 electrons.

15. 15.Describe the structure of a carbanion.

    A carbon bearing a negative charge with eight valence electrons including a lone pair. It is $sp^3$ hybridized and pyramidal (like ammonia). It is electron-rich and acts as a nucleophile / base.

    Hint: $sp^3$, pyramidal, lone pair, nucleophile.

16. 16.Describe the structure of a free radical.

    A neutral species with an odd (unpaired) electron on carbon and only seven valence electrons. It is typically $sp^2$ (planar) or shallow $sp^3$ pyramidal. Highly reactive and electron-deficient.

    Hint: Unpaired electron, 7 electrons, roughly planar.

17. 17.Define a carbene and a nitrene.

    A carbene ($:CR_2$) is a neutral divalent carbon species with six valence electrons and two nonbonding electrons (singlet or triplet). A nitrene ($:NR$) is the nitrogen analogue — a neutral monovalent nitrogen with six valence electrons.

    Hint: Divalent carbon / monovalent N, six electrons.

18. 18.What is an electrophile? Give examples.

    An electron-loving, electron-deficient species (Lewis acid) that accepts an electron pair. Examples: $H^+$, $NO_2^+$, $Cl^+$, $Br^+$, $BF_3$, $AlCl_3$, carbocations, $SO_3$.

    Hint: Electron-pair acceptor; Lewis acid; positive or e-deficient.

19. 19.What is a nucleophile? Give examples.

    A nucleus-loving, electron-rich species (Lewis base) that donates an electron pair. Examples: $OH^-$, $CN^-$, $NH_3$, $H_2O$, $RO^-$, $X^-$ (halides), carbanions.

    Hint: Electron-pair donor; Lewis base; negative or lone-pair bearing.

20. 20.Distinguish an ambident nucleophile. Give an example.

    A nucleophile with two different donor sites through which it can attack. Example: the cyanide ion $CN^-$ (attacks through C to give nitriles, through N to give isocyanides); the nitrite ion $NO_2^-$ (O or N attack).

    Hint: Two reactive sites, e.g. $CN^-$ (C or N).

21. 21.Distinguish homolytic from heterolytic bond fission.

    Homolytic: the bond breaks symmetrically, each atom taking one electron, forming free radicals ($A-B \rightarrow A^{\bullet} + B^{\bullet}$). Heterolytic: the bond breaks unsymmetrically, one atom taking both electrons, forming ions ($A-B \rightarrow A^+ + B^-$).

    Hint: Even split → radicals; uneven split → ions.

22. 22.What conditions favour homolysis vs heterolysis?

    Homolysis is favoured in the gas phase / nonpolar solvents, by heat (thermolysis) or UV light (photolysis), and by symmetric or nonpolar bonds. Heterolysis is favoured in polar solvents that stabilize ions, and by polar bonds.

    Hint: Nonpolar+light/heat → homolysis; polar solvent → heterolysis.

23. 23.Name the four main types of organic reactions.

    (1) Substitution — one atom/group replaced by another; (2) Addition — atoms/groups add across a multiple bond; (3) Elimination — atoms/groups removed to form a multiple bond; (4) Rearrangement — atoms reorganize within the molecule.

    Hint: Substitution, addition, elimination, rearrangement.

24. 24.Define electrophilic addition and give a typical substrate.

    Addition of an electrophile followed by a nucleophile across a multiple bond; typical of alkenes and alkynes (electron-rich pi bonds), e.g. addition of $HBr$ to propene. The pi bond acts as the nucleophile toward the electrophile.

    Hint: Alkenes/alkynes; electrophile attacks the pi bond first.

25. 25.Define nucleophilic substitution and give a typical substrate.

    Replacement of a leaving group by a nucleophile; typical of alkyl halides, e.g. $CH_3Br + OH^- \rightarrow CH_3OH + Br^-$. Proceeds by $S_N1$ or $S_N2$ mechanisms.

    Hint: Alkyl halides; nucleophile displaces leaving group.

26. 26.What is a carbocation rearrangement? Give the driving force.

    Migration of a hydrogen (hydride shift) or an alkyl group (with its bonding pair) from an adjacent carbon to a carbocation, forming a more stable carbocation. Driving force: formation of a more stable (higher-substituted or resonance-stabilized) cation.

    Hint: 1,2-hydride/methyl shift toward greater stability.

27. 27.Define structural (constitutional) isomerism and list its main types.

    Compounds with the same molecular formula but different connectivity. Types: chain, position, functional group, metamerism, and tautomerism.

    Hint: Same formula, different bonding; chain/position/functional…

28. 28.Distinguish chain, position, and functional isomerism.

    Chain: different carbon-skeleton arrangements (n-butane vs isobutane). Position: same skeleton, different position of substituent/functional group (1-propanol vs 2-propanol). Functional: same formula, different functional group (ethanol $C_2H_6O$ vs dimethyl ether).

    Hint: Skeleton / location / functional-group differences.

29. 29.What is metamerism? What is tautomerism?

    Metamerism: isomers differing in the distribution of carbon atoms on either side of a functional group (e.g. $C_2H_5-O-C_2H_5$ vs $CH_3-O-C_3H_7$). Tautomerism: a dynamic equilibrium between isomers differing in the position of a proton and a double bond (e.g. keto $\rightleftharpoons$ enol).

    Hint: Unequal alkyl split vs keto–enol proton shift.

30. 30.What is stereoisomerism? Name its two subtypes.

    Isomers with the same connectivity but different spatial arrangement of atoms. Two subtypes: geometrical (cis–trans / E–Z) isomerism and optical isomerism (chirality, enantiomers/diastereomers).

    Hint: Same connectivity, different 3D arrangement.

Open the interactive deck for the other 72 cards, with self-grading so the ones you keep missing come back.