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2.1Give the direction of the dipole moment (if any ) for each of the following molecules: (a) HF, (b) IBr, (c) Br 2 , (d) F 2. Answer: (a) H F ; (b) I B r 2.2 Boron trifluoride (BF3) has no dipole moment (=0). Explain how this observation confirms the geometry of predicted by VSEPR theory. Answer: B is SP 2-hybridized, so all atoms on the same plane, the center of positive charge and the center of negative charge coincide, and the molecule has no net dipole moment 2.3 Tetrachloroethene doesnt have a dipole moment. Explain this fact on the basis of the shape of Cl 2 C=CCl 2 . Answer: Cl Cl Cl Cl The shape of the tetrachloroethene is a planar, the vector sum of the dipole moment of each C-Cl bonds is zero. 2.4 Sulfur dioxide has a dipole moment, on the other had, carbon dioxide has no dipole moment. What do these facts indicate about the geometries of the two molecules? Answer: The fact that SO2 has a dipole moment indicates that the molecule is angular, not linear: S O O The fact that CO2 has no dipole moment indicates that its shape is linear, not angular: C O O 2.5 Using a three-dimensional formula, show the direction of the dipole moment of CH 3 OH. O H CH 3 net dipole 2.6 Trichloromethane (CHCl 3 , also called chloroform) has a larger dipole moment than CFCl 3 . Use three dimensional structures and bond moments to explain this fact. Answer: H C Cl Cl Cl F C Cl Cl Cl 2.7 Indicate the direction of the important bond moments in each of the following compounds (neglect C-H bonds). You should also give the direction of the net dipole moment for the molecule. If there is not net dipole moment, state that =0. (a) cis-CHF=CHF (c) CH 2 =CF 2 (b) trans-CHF=CHF (d)CF 2 =CH 2 Answer: (a) cis-CHF=CHF C C H F H F net dipole moment (b) trans-CHF=CHF C C H F F H =0. (c) CH 2 =CF 2 C C H H F F net dipole moment (d) CF 2 =CH 2 C C F F F F =0. 2.8 Write structural formulas for all of the alkenes (a) with the formula C 2 H 2 Br 2 and (b) with the formulaC 2 Br 2 Cl 2 . In each instance designate compounds that are cis, trans isomers of each other. Predict the dipole moment of each one. Answer: (a) C C Br H H Br cis-1,2-Dibromoethene C C H Br H Br trans-1,2-Dibromoethene C C H H Br Br 1,1-Dibromoethene =0 (b) C C Br Cl Cl Br cis-1,2-Dibromo-1,2-dichloroethene C C Cl Br Cl Br trans-1,2-Dibromo-1,2-dichloroethene =0 C C Cl Cl Br Br 1,1-Dibromo-2,2-dichloroethene 2.9 Write structural formulas (a) for two constitutional isomeric primary alkyl bromides with the formula C 4 H 9 Br, (b) for a secondary alkyl bromide ,and (c) for a tertiary alkyl bromide with the same formula. Answer: (a) Br Br (b) Br (c) Br 2.10 Although we shall discuss the naming of organic compounds later when we discuss the individual families in detail, one method of naming alkyl halides is so straightforward that it is worth describing here. We simply name the alkyl group attached to the halogen and add the word fluoride, chloride, bromide, or iodide. Write formulas for (a) ethyl fluoride and bromide, or iodide.... View Full Document

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