University of Sargodha BS 7th Semester, Final Term Exam 2015 Subject: Chemistry Course: Spectroscopic Methods in Organic Chemistry (Chem: 476) Time Allowed: 2:30 Hours Session: 2011-15 Maximum Marks: 60 Note: Objective la compulsory. Attempt any three questions from subjective part. Elaborate your answers with neat drawings. Unnecessary explanation must be avoided. Objective Part (Compulsory) Q.1 a) Choose the correct answer out of following questions. Q.2 2x5 i) As of May 23, 2007, it is a criminal offense in the USA to aim LASER pointers at aircraft. If aircraft windows could be tinted, what window colour can protect the pilots' eyes from a green LASER pointer? a) Blue, b) Green c) Orange d) Red e) Yellow ii) Which is the right descending order of wave number of following spectroscopic bands? a) VUV ESR>MW>IR> UV/Vis c) MW>IR>UV/Vis > VUV > ESR e) UV/Vis > VUV > IR>MW > ESR b) ESR > MW > IR > UV/Vis > VUV d) VUV > UV/Visible> IR > MW> ESR iii) What class of compounds is most likely to give a fragment ion [M-X*-28]? b) alkenes c) C-O compounds d) cycloalkanes a) alcohols iv). Which spectroscopic technique expresses spectroscopic data in 2 units (nm)? a) ESR b) MW e) amines v) Which of the following ionization technique in mass spectrometry involves the use of LASER rather highly accelerated electronic beam? a) APCI b) El c) ESI c) NMR d) Raman e) XRD d) FAB(+) e) MALDI 2x7 ii) Which mode of vibrations are IR active? iv) The VIBGYOR stands for what? b) Provide brief answers to the following questions on your answer book. i) What is an overtone? iii) What is a chemical shift (8)? v) How many type of protons are present in 2-bromobutane? vi) What is the core difference between EIMS and FAB(+)? vii) Write the names of four chambers of mass spectrometer? Subjective Part ) Explain briefly bathochromic and hypsochromic shifts? Elaborate your answer with suitable Examples. 6 b) Calculate the coupling constants (J) in Hz from following splitting pattern of a 'H-NMR signal by drawing the tree diagram (the line spacing are presented in Hain following pattern). 24 Q.3. a) What is spin-spin coupling? Support your answer with an example. b) Upon which two major factors the IR absorbance depends? Exemplify. 000 Q.4 6 42 7 5 a) The two daughter fragments of the radical cation of a heterocyclic compound 1 appear at 179 and 193 amu. Draw the structure of fragments and comment on the formation of cation(s) / radical cation(s). 6 1 2 m/z-235 amu b) How would you differentiate the following isomers by IR spectroscopy? 1) Propanone & prop-2-en-1-ol ii) Propanol & ethyl methyl ether iii) Methyl propanoate & 2-methylpropanoic acid Q.5 a) What is anisotropic effect in NMR? How it affects the chemical shift of a proton? Apply the effect on olefins, alkynes and benzene systems. b) Calculate them of isomeric chromophores 2 and 3 by Woodward-Fieser rule. 8 4 Q.6 Differentiate between soft and harsh ionization. Give a comprehensive account on different ionization techniques used in mass spectrometry to generate radical cations. 3+9