Lewis bases are electron-doners; sp-hybridized carbons are more electronegative

Question

Lewis bases are electron-doners; sp-hybridized carbons are more electronegative than sp' hybridized carbons; The eclipsed conformation of ethane is a transition state; S_N^2 reactions are promoted by polar aprotic solvents; E2 reactions require co-planarity of the C-H and C-leaving group bond; the mirror image of a molecule with one chirality center is its enantiomer; Diastereomers are non-superimposable mirror images; The 1,4-addition product of a conjugated diene is always more stable than the 1,2-addition product; Cyclic, all-conjugated structures with 4n+2 pi-electrons are expected to be aromartic; Acyclic, all-conjugated structures with 4n+2 pi-electrons are expected to be antiaromartic; Circle all the apply According to the Huckel's rule, a molecule is noaromatic if; It is not planer; It has 4 pi pi -electrons; It is not cyclic; E2 reactions; Are subject to stereoelectronic requirements; Obey the Zaitsev rule; Require strong bases; Molecules are chiral if they; Are optically active; Do not have internal mirror planes of symmetry; Have superimposable mirror images; The Diels-Alder reaction; Is stereospecifie; Is concerted; Requires electron-deficient dienophiles; Requires an s-trans conformation of the diene; Circle the most stable carbocation; Circle the most stable radical; Circle the most acidic of the following compound; cyclopentene; 2,3-dimethylcyclopentadiene; 5,5-dimethylcyclopentadiene; cyclopentylacetylene; cyclopentane; Circle the enantiomer of (2R, 3R)-2,3-diphenyl-3-bromo-2-butanol;

Explanation / Answer

1. a) True, OH- is a lewis base, and it has a non-bonding electron pair we can be donated.

b) True. sp hybridized C has 50 % s and 50% p character, while sp2 hybridized C has 33 % s and 67% p character. So, sp has more s character than in sp2. So, it is more electronegative.

c) True. The staggered form is stable conformation for ethane. So, while changing from one to another staggered form, eclipsed is a transition state in between.

d) True. Polar aprotic solvents are better for SN2 reactions because the polar protic solvents form hydrogen bonds with the nucleophile and hinder its activity.

e) False. E2 reactions occur in anti fashion. So, the two groups should be anti-coplanar.

f) True. Enantiomer is mirror image of a compound having chiral centre and is non-superimposable.

g) False. Diastereomers are non-superimposable but are not mirror images.

h) True. The 1,4-addition is thermodynamically favored. So, it is nore stable than 1,2-addition product.

i) False. the conditions for aromaticity are 4n+2 pi-electrons, are conjugated and planar. Planar is a condition for aromaticity.

j) False. Antiaromatic compounds are cyclic with 4n pi-electrons. Acyclic compounds are aliphatic compounds.

2. A. Huckel's rule: molecule is non-aromatic, if it is not planar and it has 4n pi-electrons. Answer is a and b.

B. E2 elimination reactions require anti-coplanar arrangement and require strong bases. But it does not always follow Zaytsev's rule. Answer is a and c.

C. Molecules are chiral if they do not have internal mirror planes of symmetry. if they have it, then they are called achiral. All optically active compounds need not to be chiral. They may or may not have superimposable mirror images.Answer is b.

D. In diels-alder reaction, it is stereospecific and concerted. But Dienophile need not to be electron deficient, it can be electron rich if diene is electron deficient. s-cis conformation is required for diene. s-trans is unreactive. Answer is a and b.

3. First structure is most stable carbocation because it is tertiary. Alkene having carbocation is not stable because it has double bond in it.

4. 3rd structure is most stable, because that radical is in resonace with the double bonds in bezene.

5. cyclopentyl acetylene is most acidic as it has C-C triple bond and has sp character. Answer is D.

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