Quiz 3

How many signals does the aldehyde (CH3)3CCH2CHO have in 1H NMR and 13C NMR spectra?

• five 1H signals and six 13C signals

• three 1H signals and four 13C signals

• five 1H signals and four 13C signals

• three 1H signals and six 13C signals

Which of hydrogens a-d in the following molecule gives a triplet signal in a normal 1H NMR spectrum?

• hydrogen a

• hydrogen b

• hydrogen c

• hydrogen d

What is the molecular weight of this compound?

• 29

• 87

• 54

• 15

Tags

NGSS.HS-PS1-7

Which of the following molecular formulas could correspond to the above mass spectrum?

• C₆H₅Br

• C₆H₅Cl

• C₆H₅CH₂Br

• C₆H₅CH₂Cl

What do the peaks on the mass spectrum represent?

• anions
• different isotopes
• atoms with differing numbers of electrons
• numbers of electrons

What do the heights of the peaks represent in the mass spectrum?

• number of isotopes
• relative abundance of each isotope
• average atomic mass
• charge:mass ratio

Investigate the mass spectra attached. Which peak is the most abundant?

• 90

• 91

• 94

• 92

• 96

Which of the following statements regarding NMR spectroscopy is wrong?

• NMR signals towards the left of the spectral chart correspond to larger chemical shifts.

• Chemical shifts are larger when the frequencies of the radiation which induces the nuclear transitions are higher.

• Chemical shifts are larger when shielding effects are greater.

• A hydrogen signal splits into n+1 peaks by spin-spin coupling when the number of equivalent hydrogen atoms on adjacent atom(s) is n, and no other neighbouring atoms are involved.

Which of the following statements regarding mass spectrometry is wrong?

• In a normal mass spectrometer, electron impact causes a molecule to lose an electron and become a molecular radical cation which decomposes into fragment cations and radicals.

• Only cations can be detected by a normal mass spectrometer.

• A compound whose molecules contain just one bromine atom shows two molecular ion peaks of similar intensity, one at +1 and one at -1 of the average m/z value.

• Molecular ion peaks always have even-numbered values of m/z.

Which carbon of (1)-(6) of hex-3-en-2-one has the smallest (most upfield) chemical shift in the NMR spectrum?

• C1

• C2

• C4

• C6