Molecular Weight

Molecular weight (MolWt)

The molecular weight (also called molecular mass) is the sum of the atomic masses of all atoms in a molecule, normally reported in daltons (g·mol⁻¹). It’s a fundamental physicochemical property used in filtering libraries and in drug-likeness rules. It provides crucial information about the size and bulk of a molecule. 

Descriptors.MolWt() is the function that is used to calculate the molecular weight of a compound.

You can access the Google Colab here; it contains all the code used in this tutorial: Google Colab

Before calculating the molecular weight, we need to import the correct modules first.

from rdkit import Chem

from rdkit.Chem import Descriptors

1. Calculate the molecular weight of Butane (Figure 1).

Code:

butane_smiles = "CCCC"

butane_mol = Chem.MolFromSmiles(butane_smiles)

# Calculate Molecular Weight

butane_mw = Descriptors.MolWt(butane_mol)

print(f"Molecular Weight of Butane: {butane_mw:.2f} g/mol")

2. Calculate the molecular weight of Benzene (Figure 2).

Code:

benzene_smiles = "c1ccccc1"

benzene_mol = Chem.MolFromSmiles(benzene_smiles)

# Calculate Molecular Weight

benzene_mw = Descriptors.MolWt(benzene_mol)

print(f"Molecular Weight of Benzene: {benzene_mw:.2f} g/mol")

3. Calculate the Aspirin (Figure 3).

Code:

M = "CC(=O)OC1=CC=CC=C1C(=O)O"

aspirin_mol = Chem.MolFromSmiles(aspirin_smiles)

# Calculate Molecular Weight

aspirin_mw = Descriptors.MolWt(aspirin_mol)

print(f"Molecular Weight of Aspirin: {aspirin_mw:.2f} g/mol")

4. Calculate the Aspirin (Figure 4).

Code:

butanol_smiles = "CCCCO"

butanol_mol = Chem.MolFromSmiles(butanol_smiles)

# Calculate Molecular Weight

butanol_mw = Descriptors.MolWt(butanol_mol)

print(f"Molecular Weight of Butanol: {butanol_mw:.2f} g/mol")

5. Calculate the Sodium propionate (Figure 5).

Code:

sodiumpropionate_smiles = "CCC(=O)[O-].[Na+]"

sodiumpropionate_mol = Chem.MolFromSmiles(sodiumpropionate_smiles)

# Calculate Molecular Weight

sodiumpropionate_mw = Descriptors.MolWt(sodiumpropionate_mol)

print(f"Molecular Weight of Sodium propionate: {sodiumpropionate_mw:.2f} g/mol")