19.1.1 Proton NMR

• What does NMR spectroscopy measure when atomic nuclei are placed in a magnetic field?

  Absorption of radiofrequency radiation
• Each nucleus in NMR spectroscopy has a nuclear spin
• Nuclei with even numbers of protons or neutrons possess nuclear spin.

  False
• Order the events that occur when a nucleus is placed in a magnetic field in NMR spectroscopy.

  1️⃣ Nucleus aligns with or against the magnetic field

  2️⃣ Two energy levels are created

  3️⃣ Energy difference $\Delta E$ is established
• Match the spectroscopic technique with its key feature:

  NMR ↔️ Nuclear spin

  IR ↔️ Molecular vibrations

  UV-Vis ↔️ Absorption of UV-Vis light
• What is the term for the change in resonant frequency of a nucleus due to its electronic environment?

  Chemical shift
• Protons surrounded by electron-donating groups are shielded
• Benzene protons are deshielded due to the ring current effect, resulting in a higher chemical shift.
• Match the type of proton with its approximate chemical shift in ppm:

  Methyl ↔️ 0.9

  Methylene ↔️ 1.3

  Benzene ↔️ 7.3
• NMR measures the absorption of radiofrequency radiation by nuclei in a magnetic field
• NMR spectroscopy is used to identify functional groups in organic molecules.

  False
• What is the formula for the energy difference \Delta E</latex> in NMR spectroscopy?

  $\Delta E =$$hf =$$\gamma \hbar B_{0}$
• Protons attached to electronegative groups are deshielded
• What determines the chemical shift ranges of protons in organic molecules?

  Shielding effects of electrons
• Match the type of proton with its chemical shift range in ppm:

  Methyl ↔️ 0.9 - 1.5

  Methylene ↔️ 1.2 - 2.0

  Aromatic ↔️ 6.5 - 8.0

  Alcohol ↔️ 0.5 - 5.0
• In ¹H NMR spectra, the area under each peak is called integration
• Order the peaks observed in the ¹H NMR spectrum of ethanol ($CH_{3}CH_{2}OH$).


  1️⃣ Triplet at 1.0 ppm for methyl protons

  2️⃣ Quartet at 3.5 ppm for methylene protons

  3️⃣ Broad singlet between 2.0 and 4.0 ppm for hydroxyl proton
• Analyzing ¹H NMR spectra can help determine the structure of organic molecules.
• What is the approximate chemical shift range for methyl protons in ¹H NMR spectra?

  0.9 to 1.5 ppm
• A quartet in ¹H NMR spectra typically appears at around 3.5
• Hydroxyl protons in ¹H NMR spectra produce a broad singlet between 2.0 and 4.0 ppm.
• What are the three key characteristics analyzed in ¹H NMR spectra to determine the structure of organic molecules?

  Chemical shifts, peak integration, splitting patterns
• Match the proton type with its chemical shift range in ppm:

  Methyl ↔️ 0.9-1.5

  Methylene ↔️ 1.2-2.0

  Methine ↔️ 1.5-2.5

  Aromatic (Benzene) ↔️ 6.5-8.0

  Alcohol ↔️ 0.5-5.0
• Peak integration in ¹H NMR spectra measures the number of protons in a specific environment.
• What type of splitting pattern is observed for the methyl protons in ethanol (CH_{3}CH_{2}OH</latex>)?

  Triplet
• A quartet in the ¹H NMR spectrum of ethanol appears at around 3.5
• What is the primary purpose of NMR spectroscopy?

  Determine the structure of molecules
• In NMR spectroscopy, atomic nuclei absorb radiofrequency radiation when placed in a magnetic field.
• Nuclei with odd numbers of protons or neutrons possess nuclear spin
• What is the formula for the energy difference between two spin states in NMR spectroscopy?

  $\Delta E =$$hf$
• Peaks in the NMR spectrum correspond to the resonance of specific nuclei within the molecule.
• Match the spectroscopic technique with its application:

  NMR ↔️ Molecular structure determination

  IR ↔️ Identification of functional groups

  UV-Vis ↔️ Measurement of electronic transitions
• What happens to the nuclear spin of a nucleus when placed in a magnetic field $B_{0}$?


  It aligns with or against the field
• In ¹H NMR, protons attached to electronegative groups are deshielded
• The electronegativity of oxygen in ethanol causes the hydroxyl proton to be deshielded and have a higher chemical shift.
• What is the typical chemical shift range for aromatic protons in ¹H NMR spectra?

  6.5 to 8.0 ppm
• The chemical shift values in ¹H NMR spectra are measured in units of ppm
• Protons near electron-donating groups are shielded and have lower chemical shift values.
• Match the proton type with its example structure:

  Methyl ↔️ Propane

  Methylene ↔️ Butane

  Methine ↔️ Isopentane

  Aromatic ↔️ Benzene

  Alcohol ↔️ Ethanol
• What is the example structure provided for methyl protons in the ¹H NMR chemical shift table?

  Propane