Nitrogen rule, ring rule, mc lafferty.pptx
Download as PPTX, PDF1 like1,330 views
Mc Lafferty rearangement, Nitrogen rule, Ring Rule,fragmentation rule
Nitrogen rule, ring rule, mc lafferty.pptx
- 1. Nitrogen Rule, Ring Rule, Mc Lafferty rearrangement
- 2. Content….. Nitrogen Rule Ring Rule Mc Lafferty rearrangement - Mechanism Applications
- 4. UNDERSTANDING THE NITROGEN RULE • Nitrogen Rule The nitrogen rule states that a molecule that has no or even number of nitrogen atoms has an even nominal mass, whereas a molecule that has an odd number of nitrogen atoms has an odd nominal mass. If a compound has only C, H, O, N, S, or halogens, then: Even molecular mass → No nitrogen (or an even number of nitrogen's) Odd molecular mass → One or more odd number of nitrogen's (like 1, 3, 5…)
- 5. Example: C H O (Ethanol) → Molecular mass = 46 (Even) → No nitrogen ₂ ₆ C H N (Ethylamine) → Molecular mass = 45 (odd) → Has 1 nitrogen ₂ ₇
- 7. Intro… Used to calculate the Degree of Insaturation(DOU). The Ring Rule helps us find how many rings or double bonds are present in a compound by using its molecular formula. • Degree of Unsaturation (DOU) = (2C + 2 + N - H - X) ÷ 2 • Where: • C = Number of carbon atoms • H = Number of hydrogen atoms • N = Number of nitrogen atoms • X = Number of halogen atoms (like F, Cl, Br, I)
- 8. Each of the following contributes:- 0 DOU: No rings or double bonds (eg, alkanes like propane, C3H8). 1DOU: One ring or one double bond (eg, cyclohexane, C6H12, or ethene, C2H4) 2 DOU: Two double bonds, a triple bond, or a combination of a double bond and a ring (eg, Benzene) 4 DOU: Indicates an aromatic ring system, such as benzene
- 9. Examples- 🔹 Example 1: Ethene (C H ) ₂ ₄ Formula: DoU = (2×2 + 2 - 4) ÷ 2 = (4 + 2 - 4) ÷ 2 = 1 1 double bond → Ethene has one double bond and no rings 🔹 Example 2: Cyclopropane (C H ) ₃ ₆ Formula: DoU = (2×3 + 2 - 6) ÷ 2 = (6 + 2 - 6) ÷ 2 = 1 1 ring → Cyclopropane has one ring and no double bonds 🔹 Example 3: Benzene (C H ) ₆ ₆ Formula: DoU = (2×6 + 2 - 6) ÷ 2 = (12 + 2 - 6) ÷ 2 = 8 ÷ 2 = 4 Benzene has 1 ring and 3 double bonds → total 4 DoU 🔹 Example 4: Butyne (C H ) ₄ ₆ Formula: DoU = (2×4 + 2 - 6) ÷ 2 = (8 + 2 - 6) ÷ 2 = 4 ÷ 2 = 2 Butyne has 1 triple bond → equal to 2 DoU 🔹 Example 5: Aniline (C H N) ₆ ₇ Formula: DoU = (2×6 + 2 + 1 - 7) ÷ 2 = (12 + 2 + 1 - 7) ÷ 2 = . 8÷ 2 = 4 Aniline has 1 ring and 3 double bonds (benzene ring) → total 4 DoU
- 11. Intro…… Mass spectroscopy is a technique used to determine the mass of a given molecule. The molecule is placed inside the spectrometer and ionized by high-energy electrons. After the molecules are ionized, they become radical cations that can then be sorted and weighed. When hydrogen is available at the gamma (γ) position on carbonyl compounds these compounds go through specific rearrangement due to the cleavage of multiple bonds, including the bonds at alpha and gamma (α and β) positions. This reaction is known as the McLafferty rearrangement. Fred Warren Mc Lafferty was an American chemist known for his work in mass spectrometry. He is best known for the McLafferty rearrangement reaction that was observed with mass spectrometry.
- 12. The rearrangement involves a six-membered ring transition state in which the carbonyl group pulls off the gamma proton, splitting the molecule into two pieces. These pieces consist of an enol radical cation and a neutral alkene fragment. Requirements for McLafferty Rearrangement:- -Π electrons -n electrons -γ protons
- 13. Mechanism of McLafferty rearrangement Step 1: Formation of Radical Cation A carbonyl compound with a γ-hydrogen undergoes electron ionization (−e ) ⁻ . This forms a radical cation, where the unpaired electron and positive charge are located on the molecule. The γ-hydrogen starts to shift toward the carbonyl oxygen, setting up the rearrangement.
- 14. STEP 2: Rearrangement Begins -γ-Hydrogen (hydrogen 3 atoms away from the carbonyl) shifts toward the carbonyl oxygen. -Creates enol radical cation tautomer's — these are two forms that can change into each other.
- 15. STEP 3: Formation of Fragment ion by Mc Lafferty rearrangement -The molecule breaks between the α and β carbon atoms. -It forms a charged ion and a neutral alkene (ethene). -The charged ion is detected in mass spectrometry; ethene is lost.
- 16. Exemples:-
- 17. Application:- Structural Identification in Mass Spectrometry: rearrangement is in structural elucidation using mass spectroscopy as the tool. The nitrogen rule helps determine if a molecule contains nitrogen, especially in unknown compound identification. Drug Discovery: Helps verify presence of nitrogen atoms in drug candidates (e.g., amines, amides, alkaloids). Mass Spectral Interpretation: Speeds up formula validation — e.g., odd m/z means odd number of nitrogen atoms. The ring rule calculates the degree of unsaturation (rings and double/triple bonds), useful in structural elucidation. Structure Determination: Used to predict presence of aromatic rings, alkenes, or cyclic compounds. This is a specific fragmentation pathway in mass spectrometry, especially in carbonyl compounds.
- 18. References 1. Spectrometric identification of organic compound- sixth edition, page no:14-15. 2. Organic spectroscopy- principle and applicastion Jagmohan norsoa publication. 3. Sharma Y.R. elementary organic spectroscopy principle and chemical application. 1st ed.S. chand and company itd; New Delhi: 2008.
- 19. Do you have any questions?