Key Problem Set 4 09-105 F 16 PDF

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Problem Set 4...

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___________ DUE MONDAY 10/31 IN LECTURE CIRCLE BELOW ONE TA and ONE TIME Yookie (A,B) Sikandar (C,D) Kyle (E,F) Julia (G,H)

Stephanie (I,J)

Complete the problems on the Sapling site labeled as “Problems for Problem Set 4”.

Complete the following AS WITH ALL PROBLEM SETS, PLEASE CLEARLY SHOW YOUR EXPLANATIONS AND WORK IN ARRIVING AT ANSWERS IN ORDER TO RECEIVE THE MOST PARTIAL CREDIT POSSIBLE Draw the Lewis structure for the following molecules, indicating nonzero formal charges near their applicable atoms. If equivalent resonance structures exist, draw the equivalent resonance structure(s) for the applicable molecule(s). IOF5

(b) N(O)2 ON(O) 2

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___________ DUE MONDAY 10/31 IN LECTURE CIRCLE BELOW ONE TA and ONE TIME Yookie (A,B) Sikandar (C,D) Kyle (E,F) Julia (G,H)

Stephanie (I,J)

An acid is a molecule that is an H donor. In the molecules below, the H that functions as the acid is labeled with an asterisk (*). The O-H* bond of each molecule thus breaks to leave behind an H+ and the remainder of the molecule, which has a (1-) formal charge on the O atom. The + weaker the O-H* bond is, the the acid is because an H is more easily released. Often extra stability of the resulting molecular ion after H+ is removed can be explained by the possibility of resonance delocalization of the resulting (1-) formal charge. For each molecular ion resulting from the below acids, draw the resonance structures having the same number of atoms with formal charge placement(s) of the same magnitude [i.e. only one atom having a

(1-) formal charge] For each set of resonance structures,

the structures that are equivalent.

: What are the properties of equivalent resonance structures?

Same magnitude and placement of formal charges on the same type(s) of atom(s); same number and types of bonds (is seen most for symmetrical molecules with multiple bonds What is the number of the molecule below whose corresponding (1-) molecular ion exhibits the of the (1-) formal charge?

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___________ DUE MONDAY 10/31 IN LECTURE CIRCLE BELOW ONE TA and ONE TIME Yookie (A,B) Sikandar (C,D) Kyle (E,F) Julia (G,H)

Stephanie (I,J)

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___________ DUE MONDAY 10/31 IN LECTURE CIRCLE BELOW ONE TA and ONE TIME Yookie (A,B) Sikandar (C,D) Kyle (E,F) Julia (G,H)

Stephanie (I,J)

B3N3H6, contains a hexagonal ring of alternating B and N atoms. Its experimentally determined structure indicates that all of its atoms lie in the same plane. Draw the valid Lewis structure of this molecule consistent with this structural determination. Show all nonzero formal charges on atoms. : If formal charges must be present, what must the sum of all of the formal charges equal? The overall charge on the molecule (here 0

(b) Draw the equivalent resonance structure(s) of your drawing from part (a). : What are the properties of equivalent resonance structures? Same magnitude and placement of formal charges on the same type(s) of atom(s); same number and types of bonds (is seen most for symmetrical molecules with multiple bonds

(c) Estimate the bond order of the equivalent B-N bonds.

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___________ DUE MONDAY 10/31 IN LECTURE CIRCLE BELOW ONE TA and ONE TIME Yookie (A,B) Sikandar (C,D) Kyle (E,F) Julia (G,H)

Stephanie (I,J)

(a) The molecule HN3 (atom sequence HNNN) is very explosive. The structures of the three best (octet-obeying) resonance contributors, which are nonequivalent resonance structures, are below.

(i) Use one or more of these structures to explain why this molecule is unstable. : What criteria are used to rank relative preference (stability) of resonance structures? SEE LAST PAGE OF NOTES K

(ii)

, estimate the average bond order of the N1 -N2 bond and the N 2-N3 bond (treating them separately) among the [ ]

(iii) Use a feature of one or more of the above resonance structures to explain (and support) why the experimentally determined N1-N2 bond length is longer than that of the N2-N3 bond.

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Stephanie (I,J)

N3-

(b) When HN3 reacts with water, the N-H bond breaks, and H + are formed. Draw the 3 best (octet-obeying) resonance structures for N3 -, which collectively are nonequivalent. (Note that among a

set of nonequivalent resonance structures, some of those structures may be equivalent to each other). Indicate which structure is most favored. For each of the separate N-N bonds, again estimate the average bond order. [Neglect a structure in this estimation

if it is a very poor contributor].

(c) Do you expect the experimentally determined N-N bond lengths in N 3- to be equal? Explain your answer, using the features of your resonance structures and estimated average N-N bond orders.

(d) N 3– is more stable than HN3. Use a comparison of the resonance structures estimated average N-N bond orders to explain this.

the

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___________ DUE MONDAY 10/31 IN LECTURE CIRCLE BELOW ONE TA and ONE TIME Yookie (A,B) Sikandar (C,D) Kyle (E,F) Julia (G,H)

Stephanie (I,J)

For each of the following molecules: (1) draw the most favored Lewis structure, (2) indicate its shape, (3) list its ideal bond angle(s), and (4) state whether the for the bond angle indicated in parentheses is or its ideal bond angle 1. What features of a Lewis structure are used to determine the shape around central atoms? Number of bonded atoms and number of nonbonding electron pairs (or single electrons) 2. What structural aspects cause deviations from ideal bond angles around each central atom in a molecule? Having different types of surrounding atoms or atom groups, having different bond orders (equivalent resonance structures have same bond orders), having nonbonding electron pairs or single electrons present 3. Which aspects increase and decrease bond angles from their ideal values? Nonbonding electron pairs (or single electrons) repel other electron pairs or bonds away the most. This mostly causes a decrease in ideal bond angles. Multiple bonds repel away single bonds. This causes increases or decreases from ideal bond angles, depending on what angle you consider and the shape of the molecule. Differences in atom or atom group size, particularly on surrounding atoms, have varying spatial requirements. This cause increases or decreases from ideal bond angles, depending on what angle you consider (a) XeF5+ (Faxial-Xe-F equatorial)

(b) SF 4 (Fequatorial-S-F equatorial)

(c) IBr 4– (Br-I-Br)

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___________ DUE MONDAY 10/31 IN LECTURE CIRCLE BELOW ONE TA and ONE TIME Yookie (A,B) Sikandar (C,D) Kyle (E,F) Julia (G,H)

Stephanie (I,J)

State whether each of the molecules in question 5 is polar or nonpolar. : What properties of a molecule and its bonds classify it as polar or nonpolar? Bond polarities and their magnitudes of polarities are estimated by |∆EN|. A |∆EN| > 0.4 and < 1.7 is polar. Bond polarities and shape are needed to determine whether a molecule is polar or not. If polar bonds are not oppositely positioned in the same plane, such that the approximate vector sum of the bond polarityvectors does not cancel in 3-D space , then the molecule is polar (a)

(b)

Rank the following molecules from the

(c)

to the

:

Briefly explain your answer by approximating bond and molecular polarities with differences in atom electronegativities and dipole vector “additions”, as we did in Lecture Notes M (Please use EN values from Lecture Notes J There is additional room on the next page

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___________ DUE MONDAY 10/31 IN LECTURE CIRCLE BELOW ONE TA and ONE TIME Yookie (A,B) Sikandar (C,D) Kyle (E,F) Julia (G,H)

Stephanie (I,J)

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___________ DUE MONDAY 10/31 IN LECTURE CIRCLE BELOW ONE TA and ONE TIME Yookie (A,B) Sikandar (C,D) Kyle (E,F) Julia (G,H) Consider the following 5 pairs of chemical species, labeled through (c).

AlCl3 Xe

LiF Ar

CH 3SH C 3H8

Stephanie (I,J)

through

for questions (a)

H2CO HOCH3

(CH 3)2NH XeF 2

Answer each question with: (1) one or more of the numbers above or (2) “none”. Numbers may appear in answers more than once.)

: What criteria determine the classification of interparticle (intermolecular) forces? Nature of bonding – polar covalent versus nonpolar covalent versus ionic

(a) Which pair(s), if any, interact with each other through hydrogen bonding? (b) Which pair(s), if any, interact with each other through dispersion forces as the dominant and thus only force? (c) Which pair(s), if any, interact with each other through dipole-induced dipole forces?

Which of the 2 molecules can form intermolecular H bonds (i.e. forms H bonds Show how the molecule forms H bonds with itself using structural drawings.

)?

: What specific bond(s) must be present in a molecule for it to form H bonds with another identical molecule? N-H, O-H, and/or F-H, with at least 1 nonbonding electron pair on the highly EN atom (molecules also must be polar (CH3 )2 NH

or

C5 H5N (C atoms and N atoms are in a hexagonal ring; H atoms bonded only to C atoms)

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___________ DUE MONDAY 10/31 IN LECTURE CIRCLE BELOW ONE TA and ONE TIME Yookie (A,B) Sikandar (C,D) Kyle (E,F) Julia (G,H)

Stephanie (I,J)

Which molecule has the boiling point, ClCH2CH2Cl or CH 3CH 2 Cl? Briefly explain. : (a) What interparticle forces are present in each molecule, and what criteria determine classification of these forces? Dispersion, dipole-dipole; polarity of molecule for dipoledipole; (b) What are the interparticle forces present in each molecule? Dipole-dipole (c) Will the relative strength of forces, or a differing number of a given force, govern which has the more extreme physical property (here, higher boiling point)? Differing number of the strongest force present

Circle below the molecule that has the

boiling point. Briefly explain.

: For the intermolecular force present in these molecules, what structural feature will determine the relative amount (or degree) of that force?

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___________ DUE MONDAY 10/31 IN LECTURE CIRCLE BELOW ONE TA and ONE TIME Yookie (A,B) Sikandar (C,D) Kyle (E,F) Julia (G,H)

Stephanie (I,J)

DNA’s function in cells lies in its double-helical structure with complementary bases that form H bonds to each other (See page 885 in our text). Several of those H bonds in one DNA molecule provide enough stability yet flexibility for the H bonding interaction to temporarily dissociate and thus allow DNA to unravel in order to allow its replication and other functions. The structure of one of those bases, thymine (T) is shown below. Thymine forms 2 H bonds to adenine (A) (again see p. 885; also see p. 883 for the structures of all of the bases). Tautomers are molecules that differ in the position of an H atom. The structure of a tautomer of thymine is shown below. If this tautomer, rather than the stable form of thymine, were present in a strand of DNA during its replication, draw the interaction between applicable structures showing how this tautomer would form H bonds with other base(s), thus disrupting the normal base pairing and function of DNA.

(1) What base’s structure resembles that of the tautomer the most in its number of H-bonding acceptor and donor atoms (i.e. the total number of H bonds it can form with another base)? Cytosine -like cytosine, the tautomer has one H bond “donor” and two H bond “acceptors” (i.e. two applicable atoms with nonbonding electron pairs) (2) With what base can the base of your answer in (1) form H bonds? guanine

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