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Questions and Answers

A scientist is analyzing the IR spectrum of an unknown gas to determine its global warming potential (GWP). Which of the following spectral characteristics would suggest the gas has a high GWP?

IR absorption bands primarily in the high-frequency region (e.g., >3000 cm-1).
Weak IR absorption bands that do not overlap with the Earth's emission spectrum.
IR absorption bands primarily associated with N-H stretches.
Strong IR absorption bands that closely match the Earth's emission spectrum. (correct)

Which of the following vibrational modes would you expect to find in an alkene but not in an alkane?

C=C stretches around 1640-1680 cm-1 (correct)
Broad O-H stretches around 3300 cm-1
C-H stretches around 2800-3000 cm-1
Sharp C=O stretches around 1715 cm-1

In comparing the IR spectra of an alcohol and an amine, what key difference in the O-H and N-H stretching regions (2700 - 3600 cm-1) would help distinguish them?

The amine N-H stretch will appear at a lower wavenumber than the alcohol O-H stretch.
The alcohol O-H stretch will exhibit two distinct peaks, while the amine will only show one.
The amine will have only one broad peak, while the alcohol will have two.
The alcohol O-H stretch will be broader and stronger than the amine N-H stretch. (correct)

You have two compounds: one contains a carbonyl group (C=O) and one does not. Where would you primarily look in the IR spectrum to confirm the presence of the carbonyl group?

Around 1670-1780 cm-1 for a strong, sharp peak. (C) Signup and view all the answers

Which of the following statements accurately describes the relationship between bond strength and IR absorption frequency (wavenumber)?

Stronger bonds generally absorb at higher frequencies (higher wavenumbers). (D) Signup and view all the answers

Consider an aromatic compound. Which IR absorption bands would be most characteristic and useful for identifying its aromatic nature?

C=C stretches around 1625-1450 cm-1 and C-H stretches around 3090-3000 cm-1 (C) Signup and view all the answers

You are comparing the IR spectra of cyclohexane and cyclohexene. What key difference would you expect to observe?

Cyclohexene will exhibit a C=C stretch around 1640-1680 cm-1, while cyclohexane will not. (B) Signup and view all the answers

A chemist is analyzing a compound and observes a sharp peak at 1715 cm-1 in the IR spectrum. Which of the following functional groups is most likely present in the compound?

Carbonyl (D) Signup and view all the answers

Which of the following compounds would exhibit a CΞC stretch in its IR spectrum?

Ethyne (D) Signup and view all the answers

How many N-H bands would you expect to see in the IR spectrum of a primary amine (R-NH2)?

Two (C) Signup and view all the answers

Which of the following statements best describes the role of structural elucidation in organic chemistry?

It involves determining the precise arrangement of atoms and bonds within a molecule. (A) Signup and view all the answers

How does the degree of unsaturation (DOU) relate to the structure of a molecule?

DOU corresponds to the number of $\pi$ bonds and/or rings present in a molecule. (D) Signup and view all the answers

Which of the following techniques is used by the Canadian Food Inspection Agency (CFIA) to identify potential contamination or adulteration in food products?

Infrared Spectroscopy (B) Signup and view all the answers

What is a key difference between infrared (IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy in determining molecular structures?

IR spectroscopy measures bond vibrations to identify functional groups, while NMR spectroscopy analyzes the magnetic properties of atomic nuclei to determine connectivity. (B) Signup and view all the answers

How would a chemist use the degree of unsaturation (DOU) in conjunction with spectroscopic data (IR and NMR) to determine a molecular structure?

DOU provides the number of $\pi$ bonds and rings, limiting the possible structures, while spectroscopic data identifies specific functional groups and connectivity. (A) Signup and view all the answers

Consider two organic molecules with the same molecular formula. Molecule A has a distinctive sharp peak at 1700 cm$^{-1}$ in its IR spectrum, while Molecule B shows a complex pattern of signals in the 1-2 ppm range in its $^1$H NMR spectrum. What can be inferred?

Molecule A contains a carbonyl group, while Molecule B largely consists of alkyl groups. (D) Signup and view all the answers

A compound has a molecular formula of $C_6H_{12}$. What is its degree of unsaturation?

1 (A) Signup and view all the answers

Which of the following best explains why small structural changes in organic molecules can lead to significant differences in their physiological effects?

Changes in structure can influence how a molecule interacts with biological receptors or enzymes, leading to different biological responses. (B) Signup and view all the answers

In the absence of an external magnetic field in NMR spectroscopy, how are the magnetic moments of atomic nuclei oriented?

Randomly oriented. (B) Signup and view all the answers

What happens to the magnetic moments of atomic nuclei when an external magnetic field (B0) is applied in NMR spectroscopy?

The magnetic moments align, some parallel and some opposed to B0. (C) Signup and view all the answers

An R&D scientist is trying to identify an unknown impurity, with a peak at 1730 cm-1 on the IR spectrum. Which functional group could this represent?

Carbonyl (C) Signup and view all the answers

An unknown impurity is found to have the same mass as an amphetamine sample, according to mass spectrometry. What can be concluded?

The impurity could be a constitutional isomer of amphetamine. (C) Signup and view all the answers

What is the fundamental principle behind how NMR spectroscopy works?

Atomic nuclei align in an external magnetic field and absorb radio frequency radiation. (A) Signup and view all the answers

What makes NMR spectroscopy such a powerful tool for structural elucidation of organic compounds?

It reveals comprehensive information about the magnetic environment of each atom, providing insights into the molecular structure. (A) Signup and view all the answers

How does the spinning of atomic nuclei with a positive charge influence their magnetic properties?

It creates a small, localized magnetic field known as a magnetic moment. (D) Signup and view all the answers

An organic chemist obtains both IR and NMR spectra of an unknown compound. How might these techniques be used together to elucidate the structure of the unknown compound?

The IR spectrum identifies functional groups present, while NMR reveals the carbon-hydrogen framework and connectivity. (A) Signup and view all the answers

Which statement accurately describes chemically equivalent hydrogens?

They have identical environments and share the same signal. (B) Signup and view all the answers

For a mono-substituted aromatic ring, what is the expected integration ratio of the aromatic protons?

5H (C) Signup and view all the answers

What information does the area under an NMR signal provide?

The number of hydrogen atoms represented by the signal. (B) Signup and view all the answers

If a compound exhibits two signals in its $^1H$ NMR spectrum with an integration ratio of 2:3, what does this indicate?

The compound contains two types of hydrogens, with the first type having two hydrogens and the second type having three. (C) Signup and view all the answers

What is the standard reference compound used in $^1H$ NMR spectroscopy for determining chemical shifts?

TMS (A) Signup and view all the answers

What does a chemical shift value (δ) in ppm represent in NMR spectroscopy?

The chemical environment of a proton relative to a standard compound. (B) Signup and view all the answers

Predict how many signals would be present in the $^1H$ NMR spectrum of benzene.

1 (A) Signup and view all the answers

What is the primary reason aromatic proton signals often overlap in the 7-8 ppm region of an NMR spectrum?

Aromatic protons can have very similar chemical shifts due to comparable electronic environments. (A) Signup and view all the answers

How can IR spectroscopy differentiate between acetylsalicylic acid and methyl salicylate?

Acetylsalicylic acid will exhibit a broad O-H stretch due to the carboxylic acid, while methyl salicylate will exhibit a C-O stretch from the ester. (A) Signup and view all the answers

In the provided 1H-NMR spectrum of the unknown impurity, what information can be derived from the number of signals and their integrals?

The number of signals reveals the different magnetic environments of the protons, while the integrals indicate the relative number of protons in each environment. (C) Signup and view all the answers

Given the 1H-NMR spectrum of the unknown impurity, which of the following structural features can be deduced based solely on the presence of a 5H signal?

The presence of a monosubstituted benzene ring. (D) Signup and view all the answers

Considering both MS and IR data suggest the unknown impurity is a constitutional isomer of amphetamine, and the 1H-NMR shows signals between 1-3ppm, which structural feature is most likely present?

Aliphatic protons near a carbon bearing an amine or aromatic ring. (B) Signup and view all the answers

If the unknown impurity exhibits 1H-NMR signals ‘d’ and ‘e’ integrating to 2H each, what structural element is most likely contributing to these signals?

A symmetrical ethylene group adjacent to the aromatic ring. (D) Signup and view all the answers

A compound with the molecular formula $C_8H_{10}O$ exhibits a strong, sharp IR absorption at $1682 cm^{-1}$. What degree of unsaturation is indicated by the molecular formula?

4 (D) Signup and view all the answers

A compound with the formula $C_8H_{10}O$ shows a strong, broad IR absorption at $3300 cm^{-1}$. What functional group is most likely present, based on this IR data?

Alcohol (A) Signup and view all the answers

Consider 4-nitro-3-(trifluoromethyl)aniline. How many distinct $^1H$ NMR signals would you expect to observe?

3 (A) Signup and view all the answers

For 4-nitro-3-(trifluoromethyl)aniline, which region of the IR spectrum would you expect to show major bands corresponding to the nitro group?

$1300-1600 cm^{-1}$ (B) Signup and view all the answers

A compound with formula $C_6H_{12}O_2$ exhibits a strong, sharp IR absorption at $1750 cm^{-1}$. What functional group is likely present?

Ester (A) Signup and view all the answers

A compound with the molecular formula $C_6H_{12}O_2$ exhibits a strong, sharp IR absorption at $1750 cm^{-1}$. What is the degree of unsaturation?

1 (B) Signup and view all the answers

A molecule of $C_6H_{12}O_2$ shows signals in the $^1H$ NMR spectrum at $delta$ 2.0 ppm (2H, quartet), 1.2 ppm (3H, triplet), 4.1 ppm (2H, quartet) and 0.9 ppm (3H, triplet). Which partial structure is most consistent with these signals?

$CH_3CH_2-O-C(=O)$ (B) Signup and view all the answers

A researcher obtains an IR spectrum of a synthesized compound. The spectrum shows a strong absorption at approximately $1715 cm^{-1}$. Which of the functional groups listed is LEAST likely to be responsible for this absorption?

Alcohol (A) Signup and view all the answers

Flashcards

Structural elucidation

The process chemists use to determine the arrangement of atoms in a molecule.

Spectroscopy

A technique used to collect a unique spectral "fingerprint" from a sample, useful for identifying substances or detecting contamination.