29) The structural formulas are given for these cis or trans alkenes. (a) trans-1,2-dichloropropane
Write the structural formula for:
30) In each case, tell whether cis and trans exist. If they do, write the structural formulas for two isomers and label each cis or trans, (a) Br2CH2 : No
(b) CH3CH2CH=CHCH2CH3: Yes
(c) CH3CH=CHCH3: Yes
31) Which of these molecules can have cis and trans isomers? For those that do, write the structural formulas of these two isomers and label each cis or trans. For those that cannot have these isomers, explain why. (a) CH3CH2BrC=CBrCH3
(c) CH3CH2 lC=ClCH2CH3
32) Oxalic acid has the structural formula.
Is cis-trans isomerism possible for oxalic acid? Explain your answer. No; Free rotation about the single C-C bond prevents it.
33) 2-methyl propene has the Lewis structure:
Is cis-trans isomerism possible for this oxalic acid?
34) For each pair of bonds, predict which will be the shorter. (a) B-Cl or Ga-Cl
(b) C-O or Sn-O
(c) P-S or P-O
(d) the C=C or the C=O bond in acrolein H2O=CH-C=OH
35) For each pair of bonds, predict which will be the shorter. (a) Si-N or P-O
(b) Si-O or C-O
(c) C-F or C-Br
(d) the C=C bond or the C=N bond in acrylonitrile, H2C=CH-C=N 37) Compare the nitrogen bonds in hydrazine, N2H4, and in “laughing gas” N2O. In which molecule is the nitrogen-nitrogen bond shorter? In which should the bond be longer? 38) Consider the carbon-oxygen bonds in formaldehyde, H2CO, or the bond in carbon monoxide, CO. In which molecule is the carbon-oxygen bond shorter? The bond is shorter in CO
42) Estimate ΔHº for forming 2 mol ammonia from molecular nitrogen and molecular hydrogen. Is this reaction exothermic or endothermic? (N2 has a triple bond.) -92 kj is the ΔHº, this reaction is exothermic.
44) Which of the four molecules, HF, HCl, HBr, and HI has the strongest chemical bond? Using bond energies, estimate ΔHº for the reaction of molecular hydrogen with each of the gaseous molecular halogens: fluorine, chlorine, bromine, and iodine. Which is the most exothermic reaction? Of the four molecules, HF has the strongest chemical bonds. F:538 kj, Cl:184 kj, Br:103kj, I; 11kj. The reaction with F is the most exothermic. 47) For each of these bonds, identify the more polar one and use δ+ or δ- to indicate the partial charge on each atom. (a) B-Cl and C-O
(b) O-F and O-Se
(c) S-Cl and B-F
(d) N-H and N-F
48) The molecule below is urea, a compound used in plastics and fertilizers. (a) Which bonds in the molecule are polar and which ones are nonpolar? All urea bonds are a bit polar.
(b) Which is the most polar bond in the molecule? Which atom is the partial negative end of this bond? The most polar bond is C=O. O is partially negative.
79) The C-Br bond length in CBr4 is 191 pm; the Br-Br distance in Br2 is 228 pm. Estimate the radius of a C atom in CBr4. Use this value to estimate the C-C distance in ethane, H3C-CH3. How does your calculated bond length agree with the measured value of 154 pm? Are radii of atoms exactly the same in every molecule? 82) The molecule pictured below is acrylonitrile, the building block of the synthetic fiber Orlon. (a) Which is the shorter carbon-carbon bond?
The C=C bond is shorter.
(b) Which is the stronger carbon-carbon bond?
The C=C bond is stronger.
(c) Which is the most polar bond and what is the partial negative end of the bond? C double bonded to N is the most polar and the N is partially negative. 85) Arrange these bonds in order of increasing length (shortest first). List all the factors responsible for each placement: O-H, O-O, Cl-O, O=O, O=C.
September 29, 2009
Chem 131 Section 1
8.8 – 8.11
52) Write correct Lewis structures and assign a formal charge to each...
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