2 (I) Circle the letter of the correct answer. (5 pts each) (1) Which of the following statements about the physical properties of organic molecules is false? (a) The substitution of a methyl group for a hydrogen at an alkane causes an increase in the boiling point of the molecule. (b) The boiling point of a linear alkane increases with increasing chain length. (c) The substitution of an HO- group for a hydrogen at an alkane causes an increase in the boiling point of the molecule. (d) The boiling point for alkanes of constant molecular weight increases with increasing branching. (e) The boiling point for alkanes of constant molecular weight decreases with increasing branching. (2) Which of the following statements about valence bond resonance structures is true? (a) Contributing valence bond resonance structures with a minimum number of octets at the individual atom will make the largest contribution to the overall structure. (b) In cases where a positive charge is delocalized over two or more atoms, the charge will lie preferentially at the atom that is most electronegative. (c) Contributing valence bond resonance structures with a maximum formal charge at the individual atoms will make the largest contribution to the overall structure. (d) In cases where a negative charge is delocalized over two or more atoms, the charge will lie preferentially at the atom that is most electronegative. (e) All of the statements are true. (3) What is the correct IUPAC name for the following compound? (a) 2,5-dimethyl-4-(isopropyl)hexane (b) 2,6-dimethyl-4-(isopropyl)heptane (c) 2,5-dimethyl-4-(isopropyl)heptane (d) 2,4-dimethyl-3-(1-methylpropyl)hexane (e) None of the answers are correct (4) Which of the following bonds has the smallest bond dissociation energy? CH3CH2H(a)CH2HCH3HCH3HHCH3H(c) (d)(e)(b) (5) Which of the following molecules has no trans isomer? (a)(c)(d)(b)(e)MeMeMeMeMeMeCl FMeHHHMeH3 (6) Which of the following molecules contains no sp3-hybrid orbitals? (7) How many equatorial hydrogens are there at the most stable chair form of cis-1,4-dimethylcyclohexane? (a) 2 (b) 3 (c) 4 (d) 5 (e) 6 (8) Which of the following reactions is not part of a free radical halogenation reaction mechanism? (a)Cl ClCl2+(b)CH3CH3Cl + ClHClCl2(c)ClCH4CH3(d)Cl+CH3II+CH3Cl(e)Cl2hνCl Cl++++ (9) How many tertiary-type hydrogens are there in the following molecule? (a) 2 (b) 4 (c) 6 (d) 9 (e) 12 (10) Which of the following molecules has polar covalent bonds but no net dipole moment? CH3(a)(c)(d)(b)(e)CH3COOCCl4H2OH HCH3CH2CHCH2CH3CH2CH2CHCH3CH3(a)(c)(d)(b)(e)HClCCl4CH4CH3CH2ClNH34 (11) Circle the alkane that will give only a single product from a free radical monobromination reaction. CH3CH3CH3CH3CH3CH3HCH3HCH3HCH3CH3CH2CH3 (12) Circle the cycloalkane that has the highest heat of combustion per –CH2- group.5 (II) Write the IUPAC names for the following molecules. (A) (5 pts) 3,4-dimethylhexane (B) (10 pts) 5-t-butyl-3-methyl-4-propyloctane123456786 (III) (A) Write all of the products of monochlorination of the following alkane. (10 pts) (B) The relative reactivity of 3o, 2o, and 1o alkane hydrogens in free radical chlorination reactions is 6 (tertiary):4 (secondary):1 (primary). Calculate the fractional yield of any one of the products in question III (A) above. (10pts) € % A = (12)(1)(12)(1) + (2)(4) + (2)(6) = 12/32% B = (2)(4)(12)(1) + (2)(4) + (2)(6) = 8/32% C = (2)(6)(12)(1) + (2)(4) + (2)(6) = 12/32CH3CCH3HCH2CCH3CH3HCH3CCH2ClHCH2CCH3CH3HCH3CCH3HCHClCH3CCH3ClCH2CCH3CH3HCCH3CH3HA B C7 (IV) Answer each of the following questions in 5 words or less. (3 pts each) (A) What is the hybridization of the carbon atoms in the following molecule? C C HH sp (B) What is the name given to the attractive forces that hold alkanes in the liquid or gas state? London forces or Van de Waal forces (C) Which is the only cycloalkane in which all of the carbons lie in a single plane in the most stable conformation? Cyclopropane (D) Which cycloalkane has the least total ring strain? Cyclohexane (E) Name one of the three types of ring-strain discussed in class. Bond angle strain Torsional strain Transannular strain8 (V) (A) Draw the two chair forms of trans-1,2 dimethylcyclohexane. (10 pts) (B) Circle the chair form that is most stable overall. (5 pts) (C) Place a star next to the chair form that is destabilized by interactions between gauche methyl groups at the cylcohexane ring. (5 pts) HMeHMeHMeHMe9 (VI) (A) Write the Newman projection for the most stable conformer of 1,2 dichloroethane (5 pts) (B) Write the structure of the boat form of cyclohexane and explain why this structure is so much more unstable than the chair form. (5 pts) (1) Destabilizing “flagpole type interactions between hydrogen at the 1 and 4 carbons. (2) Strong eclipsing [torsional] strain between substituents at the four carbons at the bottom of the boat.ClHHHHClH HHH HHHHHH10 (C) (i) Circle the hydrogen atom transfer reaction that proceeds through the most advanced (“latest”) reaction transition state. (2 pts) CH3HBr•HBrCH3•+CH3HCl•HClCH3•+++ (ii) Briefly explain your answer. (8 pts) The bromine radical is kinetically less reactive than chlorine radical because the reaction of Br• is uphill thermodynamically, while the reaction of Cl• is thermodynamically favorable. The Hammond postulate states that thermodynamically unfavorable reactions proceed through later [more product like] transition states than thermodynamically favorable reactions. This can be illustrated on a free energy profile, but this is not required to receive full credit for your