ochem week 9 part 1

Quartet

A splitting pattern in NMR resulting from a hydrogen atom seeing three equivalent neighboring hydrogens.

Triplet

A splitting pattern in NMR resulting from a hydrogen atom seeing two equivalent neighboring hydrogens.

Singlet

A peak in NMR that does not split, indicating that a hydrogen atom has no neighboring equivalent hydrogens.

Diastereotopic Hydrogens

Hydrogens that are in different environments in a molecule, causing them to have different NMR signals.

Chemical Environment

The unique surroundings of an atom in a molecule, influencing its NMR signal.

Prochirality

A property of a molecule that can become chiral upon the replacement of a specific atom or group.

Magnetic Anisotropy

The variation of magnetic properties in different directions within a molecule, often affecting NMR chemical shifts.

Degree of Unsaturation

A measure of the number of rings and double bonds in a compound, calculated from the molecular formula.

Steric Hindrance

The effect of the spatial arrangement of atoms affecting the reactivity and properties of a molecule.

What indicates larger peaks in HNMR?

Larger peaks indicate either more chemically equivalent carbons or a greater number of hydrogen atoms attached.

What is the significance of an integration value of 4 or larger in HNMR?

An integration value of 4 or larger suggests more than one carbon is attached to the hydrogen associated with that peak.

How do hydrogen atoms appear in HNMR if not attached to a carbon?

All hydrogen atoms in a molecule will show up even if not attached to a carbon; for example, an alcohol with two carbons won't split, and other hydrogens will become a quartet.

What is the chemical shift range for aldehydes in HNMR?

Aldehydes typically appear in the range of 9-10 ppm.

What are homotopic hydrogens in 1H NMR?

Homotopic hydrogens are considered electronically equal and may show identical signals in 1H NMR.

What is prochirality in relation to HNMR?

Prochirality refers to hydrogens that become prochiral when one hydrogen is replaced, making a specific R or S asymmetric center.

What does magnetic anisotropy refer to in NMR?

Magnetic anisotropy relates to a different type of shielding where circulating electrons generate opposing magnetic fields to the external magnetic field.

NMR (Nuclear Magnetic Resonance) Peak Representation

All hydrogens in a molecule are represented in NMR, even if not directly attached to a carbon.

Hydrogen Splitting Patterns

For alcohols with two carbons, they do not split; other hydrogens can appear as a quartet.

Integration Number Significance

A peak with an integration number higher than 4 usually indicates multiple carbons attached.

Chemical Shift PPM for Aldehydes

Aldehyde signals are typically found at 9-10 ppm.

Chemical Shift PPM for Carboxylic Acids

Carboxylic acid signals are generally located at 10-12 ppm.

Arene Hydrogen Peak Shift

Arene hydrogens are usually found between 6-8 ppm, depending on their environment.

Symmetrical Arene NMR Peaks

In a 1,4 arene, there will be two distinct peaks due to symmetry among neighboring hydrogens.

Multiplet Formation in Arenes

Closer hydrogens in arenes can merge into a multiplet instead of appearing as distinct peaks.

What are homotopic hydrogens in 1H NMR?

Homotopic hydrogens are considered electronically equal in 1H NMR.

What would happen if homotopic hydrogens were replaced by deuterium?

They would no longer be considered homotopic and could become prochiral.

What is prochirality in terms of hydrogen atoms?

Prochirality refers to the situation where replacing one hydrogen creates a specific R or S asymmetric center, resulting in an enantiomer.

What are diastereotopic protons?

Diastereotopic protons are formed when replacing hydrogen creates a diastereomer.

What is magnetic anisotropy?

Magnetic anisotropy relates to a different type of shielding in NMR, caused by circulating electrons generating an opposing magnetic field.

What does a peak at 3050 cm-1 indicate?

A peak at 3050 cm-1 indicates the presence of an alkene.

What does a peak at 2950 cm-1 signify?

A peak at 2950 cm-1 signifies the presence of CH groups.

What does a peak at 1690 cm-1 represent?

A peak at 1690 cm-1 represents C=O bonds.

What does a peak at 1520 cm-1 indicate?

A peak at 1520 cm-1 indicates the presence of C=C bonds.