Multiple Choice (2 pts. each) The compound CH3NH2 contains a C-N bond. Which of

Question

Multiple Choice (2 pts. each) The compound CH3NH2 contains a C-N bond. Which of the following describes the charge on the nitrogen in this compound? 1. Which of the following molecules 5. contains an atom that has an incorrect designation of its formal charge? A. D) uncharged A) +1 B) slightly positive E) -1 C) slightly negative B. 6. Which compound is not an isomer of the Ha others? CNN 2. What is the hybridization of the carbon that is attached to the oxygens in CH,COOH (acetic acid)? A. sp B. sp C.sp D. sp E. none 3. Which molecule has the greatest dipole A, I B. Il C.Ill DJV E' None moment? 7. The structure of propofol, a widely used anesthetic, is shown below. How many sp3 hybridized atoms are in this compound? C.CH2Br2 A, CHC2 D. CF B.CC14 E. CH2F2 4. What hybrid orbitals are used to form the sigma bond between C-1 and C-2 respectively, in the structure shown below? A. 1 B.5. C.6 D.7 E.9 CH Which compounds have a nonzero dipole moment? A) CCI4 B) CO2 C) CH30CH3 D) (CH3)2C-C(CH3)2 E) BCl3 8. HC-CH-C-CEN and sp A) sp'and B) sp and sp D) sp and sp

Explanation / Answer

1. (C) Should also contain a positive(+1) charge on the central nitrogen atom and a negative charge(-1) on each terminal nitrogen atom.

2. (C) In the structure of CH3COOH, the carbon is attached to one oxygen by sigma and pi-bond, to other oxygen by sigma bond and to methyl group by sigma bond. So, there are 3 sigma bonds and the hybridisation is therefore sp2. 3. (E) The bond polarity of CCl4 and CF4 get cancelled due to symetrical tetrahedral shape and these have zero dipole moment. The electronagativity of fluorine, chlorine and bromine is 4.0, 3.0 and 2.8 respectively and that of carbon is 2.5. The electronegativity difference of carbon and fluorine bond is highest, so the polarity is highest. Hence, the order of dipole moment is CH2Br2<CH2Cl2<CH2F2 . 4. (C) The first carbon(C-1) is sp2 hybridised (3 sigma and 1 pi bond) and C-2 is sp hybridised (2 sigma and 2 pi bonds).    5. (C) This is so because nitrogen is more electronegative than carbon and will attract the electrons towards itself and becomes slightly negatively cahrged. 6. (A) Isomers have different structural formula but same molecular formula. The molecular formula for II, III and IV is C4H8O whereas for I it is C4H6O.    7. (C) The carbons with 4 sigma bonds are sp3hybridised. In this structure the sp3hybridised carbons are those which are linked as iso-prpyl side cahins to the ring.    8. (C) In (D) there is no difference in electronegativity and hence no polarity. In (A), (B) and (E) the polarity cancel out due to symmetrical molecule . In (C), the oxygen attract electrons towards itself from the methyl groups and has net permanent dipole moment.

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