[SOLVED] CHMS 5030 Molecular Analysis MIDTERM Assignment

MIDTERM Assignment

CHMS 5030: Molecular Analysis

Part 1: Basic Concepts (50 pts)

Q 1: Which wavelength (meter) could be used by Infra-Red (IR) spectrometer? (2 pts)_______.

A) 10-10 m

B) 10-9 m

C) 10-7 m

D) 10-5 m

E) 10-3 m

Q 2: A carbonyl C=O bond vibrates at 1710 cm-1 in IR spectra. What is the frequency in Hertz of light this carbonyl C=O absorbs (IR)? (2 pts)_______.

A) 5130 ×1012 Hz

B) 5130 ×109 Hz

C) 5130 ×1010 Hz

D) 5130 ×1011 Hz

Q 3: Which vibration mode will give rise to the highest absorption frequency for a C-H bond in Infrared spectrum (IR)? (2 pts)_______.

A) Symmetric stretching

B) Asymmetric stretching

C) Scissoring

D) Twisting

E) Rocking

Q 4: If a carbonyl C=O bond vibrates at 1715 cm-1 in the IR spectrum. What is the overtone of this carbonyl (2 pts)_____.

A) 3430 cm-1

B) 2230 cm-1

C) 1715 cm-1

D) 857 cm-1

Q 5: In the IR spectrum, which covalent bond has the lowest stretching frequency according to Hooke’s Law? (2 pts )___________.

A) C-O.

B) C-H.

C) C-Br.

D) C-N.

Q 6: In the IR spectrum, the calculated O-H stretching wavenumber is 3553 cm-1
, what is the stretching frequency of O-D (Oxygen-deuterium bond)? (O-H and O-D have the same Force Constant) (2 pts )_____________.

A) 3553 cm-1

B) 3053 cm-1

C) 2585 cm-1

D) 2085 cm-1

Q 7: In the IR spectrum, a carbonyl (C=O) stretching frequency was observed at 1685 cm-1
. Which type(s) carbonyl it might be______________? (2 point)

Q 8: In the IR spectrum, a strong broad band near 3200 cm-1
is observed. Which of the following compound(s) is least likely to give rise to this band. (2 pts)_______.

Q 9: In the IR spectrum, which of the following covalent bond(s) will have the lowest intensity of its stretching frequency_________? ( 2pts)

A) C-O

B) C-C

C) C-H

D) C-N.

Q 10: In the IR spectrum, which of the following lactam carbonyl (C=O) vibrates at the highest stretching frequency _________? ( 2pts)

Q 11: Which fragments or molecules could NOT be observed in the Mass Spectrum? (2 pts)________.

Q 12: If a mass spectrum of morphine is requested to provide the molecular weight (MW 285), which of the following ionization method will be suitable (2 pts)____________.

A) EI

B) CI

C) ESI

D) MALDI

Q 13: Which of the following reagents would cause less fragmentation when it is used in the chemical ionization (2 pts)____________.

A) H2 (hydrogen)

B) CH4 (methane)

C) i-C4H10 (isobutane)

D) NH3 (ammonia)

Q 14: Calculate the degree of unsaturation for the following formula (2 pts).

A) C17H19NO3: ________________________

B) C47H51NO14:_______________________

C) C7F5ClO:__________________________

D) C5H9BrMgSi:________________________

Q 15: In the MS spectrum (EI) for a small organic compound, it is found that the molecular ion peak is at m/z 285 with 85% relative intensity. The peak at m/z 286 has 15.8% relative intensity. Please propose a possible formula for this organic compound (2 pts)______.

A) C20H29O

B) C19H27NO

C) C18H21O3

D) C17H19NO3

Q 16: In the MS spectrum (EI) for a small organic compound, it is found that the molecular ion peaks are at m/z 183 (100% relative intensity), m/z 184 (7.6% relative intensity), m/z 185 (97% relative intensity), and m/z 186 (7.4% relative intensity). Please propose a possible formula for this organic compound (2 pts)______.

A) C7H5BrO

B) C13H28

C) C7H14Cl2O

D) C6H12Cl2ON

Q 17: Use “Thirteen rule” to determine the molecular formula of an organic hydrocarbon compound (containing only H and C) with the molecular ion peak at m/z 100 in the Mass spectrum? (2 pts)____.

A) C7H16

B) C8H4

C) C6H12

D) C7H14

Q 18: An organic compound is determined with high resolution mass spectrum that shows the molecular ion peak at m/z 285.1367 using electron ionization, which of the following formula is possible for this compound? (2 pts)____.

A) C19H27NO m/z 285.2086

B) C18H21O3 m/z 285.1485

C) C17H19NO3 m/z 285.1365

D) C20H29O m/z 285.2211

Q 19: In the mass spectrum, the fragmentation process is usually complicated, but some general trends have been observed. Which of the following fragmentation pathway(s) will be generally favored (2 pts)_________.

Q 20: Which of the following fragmentation can NOT occur in the MS using Electron Impact ionization? (2 pts)_________________.

Q 21: Which of the following nucleus can be detected by NMR? (2 pts)_________________.

A) 13C

B) 12C

C) 16O

D) 17O

E) 14N

F) 15N

Q 22: For a 600 MHz proton NMR machine, at what frequency that 13C will absorb? (2 pts)______.

A) 100 MHz

B) 150 MHz

C) 200 MHz

D) 250 MHz

E) 300 MHz

Q 23: An increase of scan number is the most common approach to increase the NMR sensitivity. If scan number increases 100 times, how many times of sensitivity can be increased (2 pts)_____.

A) 100

B) 80

C) 50

D) 10

Q 24: A proton resonates at 2.5 ppm in a 400 MHz NMR machine, what frequency in Hertz of this proton is observed in a 600 MHz machine? (2 pts)_____.

A) 1000 Hz

B) 1200 Hz

C) 1500 Hz

D) 2000 Hz

Q 25: In 1H-NMR spectrum, the aldehyde proton (-CHO) resonates at a very high frequency, ca. 10 ppm. Which of the following factor(s) contribute(s) to such high frequency (2 pts)_____.

A) Strong hydrogen bonding

B) High electronegativity of oxygen

C) Diamagnetic anisotropy of π-bond

D) Electron delocalization

Part 2. Spectra Analysis (50 pts)

Question 26: Each of the following IR spectra is associated with one of the compounds below. Identify the compound I-V associated with each spectrum A-E. Please indicate the key functional groups near the corresponding vibrating bands (10 points). Please provide rationalization details on the space aprovided or additional page.

Question 27: A small molecule with formula of C4H9NO was determined by IR spectral analysis as provided below. Please propose a possible structure with rationalization (10 points).

Question 28: The mass spectra of 4-heptanone was provided below using electron ionization method. Please draw fragmentation mechanisms to rationalize the fragments at m/z 99, 86, 71, and 43 (10 pts).

Question 29: The mass spectra of cyclohexanone was provided below using electron ionization method. Please draw fragmentation mechanisms to rationalize the fragments at m/z 68, 55, and 42 (10 pts).

Question 30: The 1H-NMR spectrum of 4-methoxybenzaldehyde was provided below. Please assign the proton signals to the structure and provide full rationalization (10 pts).