ochem week 8 part 1

Nuclear Magnetic Resonance (NMR)

A spectroscopic technique used to determine the connectivity and environment of nuclei in a molecule.

Electronic Shielding

The phenomenon where the electronic environment around a nucleus affects its magnetic resonance signal; more electron density results in a lower chemical shift.

Chemical Shift

An indicator of the environment surrounding a nucleus, measured in parts per million (ppm) in NMR spectroscopy.

Chemically Equivalent Carbons

Carbons that have the same electronic environment and will absorb at the same chemical shift in NMR.

Downfield

Refers to regions on an NMR spectrum where there is a higher chemical shift, indicating less shielding and more electronegative environments.

Upfield

Refers to regions on an NMR spectrum where there is a lower chemical shift, indicating more shielding and higher electron density around the nucleus.

Carbon-13 NMR

A type of NMR that specifically looks at the magnetic properties of carbon-13 nuclei to provide information about carbon environments.

Proton NMR (H NMR)

A type of NMR that investigates the magnetic properties of hydrogen nuclei, giving insights into hydrogen environments in a molecule.

Depth Experiment (DEPT)

A technique in NMR that helps correlate the number of protons in a carbon environment, distinguishing between methyl, methylene, methine, and quaternary carbons.

Peak Intensity in NMR

The height of a peak in an NMR spectrum, which generally correlates to the number of protons contributing to that signal, though influenced by molecular environment.

Functionality

Refers to the specific reactive groups (like OH, CO, etc.) present in a molecule that can be identified using spectroscopic techniques.

NMR Spectroscopy

Nuclear Magnetic Resonance (NMR) spectroscopy is an analytical technique for determining the structure of organic compounds by analyzing nuclear spin in a magnetic field.

Chemical Shielding

The local electronic environment affects a nucleus's magnetic shielding; shielded nuclei have higher field (upfield) signals, while deshielded nuclei have lower field (downfield) signals.

Chemically Equivalent Carbons

Chemically equivalent carbons appear at the same position in an NMR spectrum due to their similar electronic environments.

Carbon NMR Chemical Shifts

Typical chemical shift ranges in Carbon NMR include: Carbonyl (C=O): 160-220 ppm, Alkene (C=C): ~100-150 ppm, Aromatic Carbons: ~100-160 ppm, Sp3 Carbons (C-C): ~0-70 ppm.

Downfield and Upfield in NMR

Downfield refers to higher ppm (chemical shift), indicating deshielded nuclei, while Upfield refers to lower ppm, indicating shielded nuclei.

What are chemically equivalent carbons?

Chemically equivalent carbons must have the same electronic environment and will absorb at the same chemical shift in NMR.

What does downfield indicate in NMR?

Downfield refers to regions on an NMR spectrum where there is a higher chemical shift, indicating less shielding and more electronegative environments.

How do unique carbons differ in NMR?

Unique carbons will have different electronic environments and thus will appear at different chemical shifts in an NMR spectrum.

How are chemically equivalent carbons counted in NMR?

When chemically equivalent, they are counted together with one number; however, only two carbons can be merged into one number in NMR analysis.

What does a plane of symmetry imply in NMR peaks?

A plane of symmetry can lead to equivalent chemical environments, allowing certain carbons to produce the same signal in the NMR spectrum.

What happens if extra carbons are present in a peak graph?

In an NMR spectrum, there cannot be any extra carbons; the graph will show fewer peaks corresponding to the actual number of unique carbon environments present.

What does DEPT NMR determine about carbons?

DEPT NMR determines the amount of hydrogens attached to a carbon, categorizing them into methyl (CH3), methylene (CH2), methine (CH), and quaternary (C) based on hydrogen count.

What is the difference between quaternary carbon and primary carbon?

Quaternary carbon is based on hydrogen count and has 0 hydrogens, while primary, secondary, and tertiary carbons are defined by the number of attached hydrogen atoms.

How can you differentiate primary, secondary, tertiary, and quaternary carbons in NMR?

These carbons cannot be differentiated on a typical 13C NMR but can be distinguished using a series of different DEPT spectra, such as DEPT-90 and DEPT-135.

What does DEPT-90 show in NMR?

DEPT-90 shows peaks corresponding to carbon atoms with one hydrogen (CH) specifically.