Question

1. How many sp hybridized carbon atoms are present in the following molecule? (A) 3 (B) 4 5 н.с (D). 6 2. Which bond is the longest in the following molecule? (A) (B) CECH (C) (D) 3. Which of the following molecules is chiral at room tempernture (25 C)? (A) 1,1-dimethylcyclohexane (B) cis-1,2-dimethyleyelohexanc (C) trans-,3-dimethyleyclohexane (D) trans-1,4-dimethylcyclohexane 4. Which group is an aldehyde? н н (C) (D) (A) (B) OH 5. Which group will have the highest A-value? (An A-value is the AG difference for a monosubstituted cyclohexane with a given substituent in the axial vs. equatorial arrangement.) (B) s (A) (C) (D) 6. Which experimental evidence would not support the Sx2 mechanism for the reaction between (S)-2-bromooctane and sodium acetylide (aka ethynylsodium)? (A) Only (S)-3-methyl-1-nonyne is observed as a product (B) The reaction rate decreases tenfold when the concentration of bromooctane is reduced from 1.0M to 0.1 M (C) The reaction rate doubles when the concentration of sodum acetylide is doubled. (D) The rate of reaction is increased by switching from sodium to potassium acetylide. 7. Which alcohol must undergo a rearrangement upon reaction with catalytic sulfuric acid to form an alkene? Он он OH но. (A) (B) (D) (C) 8. Which alkene is the most reactive towards bromine at room temperature? AHayd (in kcal/mol) for each alkene is provided in parentheses. 2-methylpropene (A) 2,3-dimethylbut-2-ene (B) (C) (D) ethene propene (25.7) (-32.5) (-27.8) (-29.9) 9. Which compound will react the slowest in an E2 reaction? D Br Br Br Br (в) (C) (D) (A) D D 10. Which mechanism is consistent with the formation of anti addition products from the reaction of H-Br with alkenes? (A) Formation of a brominium ion intermediate followed by ring opening (B) Concerted reaction of one molecule of H-Br with one molecule of alkene

can questions 1-9 please be answered and why are they the answer

Answer 1

1) 4 sp² carbons (as indicated below). The other carbons are either sp³ or sp carbons

sp2 1. How many sp' bybridized carbon atoms are present in th (A) 3 sp² - sp²// (B) & sp2 =C=0 (C) 5 H, (D) 6 *2. Which bond is the loneest in the following m e

2) Single bonds are longer than double bonds which in turn is longer than a triple bond. Therefore, the longest bond is bond A given in the figure.

3) 1,1-dimethylcyclohexane has two identical groups on the same carbon and hence is not chiral. Cis-1,2-dimethylcyclohexane is not a chiral compound since it has a plane of symmetry. trans-1,4-dimethylcyclohexane is not chiral since it has a plane of symmetry (the plane perpendicular to the molecule passing through C-1 and C-4). trans-1,3-dimethylcyclohexane is chiral

4) Group C is aldehyde. Group A is formate. Group B is carboxylic acid.

5) A value will be higher for the bulkiest substituent (since $\Delta$G of the equatorial isomer will be much less than that of $\Delta$G of axial isomer). Of all the groups listed above, t-butyl group is the bulkiest (in fact C(CH3)3 has higher A value than Si(CH3)3). Hence option (a) is the answer.

6) Option (a). Reaction of S-2-bromooctane with acetylide will give the R-isomer (since S_N² proceeds with inversion of configuration)

7) Option D. Upon addition of sulfuric acid to option (D) which is a primary alcohol, leads to the formation of a primary carbocation (which is unstable) and hence undergoes 1,2-alkyl shift to form a more stable secondary carbocation which undergoes deprotonation to give an alkene.

1 2 Casheraton (moestekle) Carbocation (nerschle)

8) Ethene gives more energy towards hydrogenation, therefore it is the least stable. Hence ethene is most reactive towards bromination.

9) Option D. In this compound, the Br and H (on adjacent carbon) are cis to each other. For E2 elimination to occur fast, H and Br have to be trans to each other. In this compound there are no hydrogens (in the adjacent carbon) which is trans to Br and hence the reaction will be the slowest.