ochem week 6 part 2

Mass Spectrometry

A method that measures the mass-to-charge ratio of ions to determine molecular weight and molecular formula.

Molecular Ion

The ion representing the molecule as a whole, typically the highest mass peak in mass spectrometry.

Base Peak

The most abundant peak in a mass spectrum, representing the ion detected in the greatest relative abundance.

Cation

A positively charged ion that forms when an atom loses one or more electrons.

Radical Cation

A positively charged ion that has an unpaired electron, often formed in mass spectrometry.

Fragmentation

The process by which a molecule breaks into smaller pieces during mass spectrometry.

m/z

The mass-to-charge ratio of ions; often used as a notation in mass spectrometry.

Degree of Unsaturation

A calculation that indicates the number of rings and/or multiple bonds in a molecule.

Rule of 13

A method for deriving the molecular formula from the molecular ion peak in mass spectrometry by dividing the molecular weight by 13.

Relative Abundance

The proportion of a specific ion detected in mass spectrometry relative to the most abundant ion.

Nitrogen Insertion

The addition of a nitrogen atom into a molecular structure, which can increase the number of hydrogens.

Halogens

Elements from Group 17 of the periodic table, such as fluorine, chlorine, bromine, and iodine, that often replace hydrogen in organic compounds.

Hydrocarbon

An organic compound composed entirely of hydrogen and carbon.

Oxygen's role in Unsaturation

Oxygen does not contribute to the degrees of unsaturation; it merely replaces a hydrogen without affecting saturation.

Degree of Unsaturation

The number of hydrogen atoms missing from a fully saturated molecule, determined by counting pi bonds and rings.

Molecular Formula Calculation Steps

To find molecular formula from mass spectra: Step 1: MW (m/z)/13 = Carbons; Step 2: Remainder + Carbons = Hydrogens.

Finding Molecular Formula with Oxygen

To find the molecular formula when oxygen is present: Step 1: Follow the same steps as hydrocarbons. Step 2: Replace 1 carbon and corresponding hydrogens (for O, typically replace 1 C and 4 Hs).

Molecular Weight Replacement

When calculating the molecular formula with different atoms, replace carbon and hydrogen according to the atomic weight of the substituent (e.g. 1 O replaces 1 C and 4 H).

Carboxylic Acid Adjustment

For carboxylic acids (COOH), subtract twice to account for the presence of two oxygen atoms in molecular formula calculations.

Finding Molecular Formula with Nitrogen

Step 1: Divide the molecular weight (m/z) by 13 to calculate the number of Carbon atoms (C). Step 2: Add the remainder from Step 1 to the number of Carbons to find the total number of Hydrogens (H). Step 3: Nitrogen often adds an additional hydrogen into the formula, altering it. Final Formula: C_nH(2n + 2 + #N), where #N is the number of nitrogen atoms present. Each nitrogen atom contributes one additional degree of unsaturation.