Mass spectrometry

This are topic is organic chemistry

1. Shri. Shivaji collEge Of arts, commerce, and science, akola Presented by Miss. Ankita R. Gajabhiye Msc 2 nd year (Sem 3 rd ) chemistry mass Seminar Topic : Mass Spectroometry Seminar topic : mass spectroometry

2. Content Introduction Basic principle Theory Instrumentation Fragmentation Mclafferty Rearrangement

3. Introduction Mass spectrometry is an analytical technique that measure the mass to charge particles. It is used for determining masses of particles for determining the elemental composition of a sample or molecule. Mass spectrometry is a powerful technique for identifying unknown compound, studying molecular structure, and probing the fundamental principles of chemistry.

4. Basic principles It is a most accurate method for determining the molecular mass of the compound and elemental composition. In this technique, the compound under investigation is bombarded with beam of energetic electrons. The molecules are ionised or dissociate into several fragments, some of which are positive ions. Each kind of ions has a particular ratio of mass to charge i.e m/e ratio.

5. For neopentane m/e ratio is 72

6. Theory A mass spectrum consist of an array of peaks of different heights. The nature of the spectrum is dependent on properties of the molecule, ionisation potential, sample pressure and the instrument design. The mass spectrometer bombards a molecule M with high energy electrons. M+e – ----------->  M +  + 2e –

7. Mass spectrum Of neopentane

8. Instrumentation

9. Fragmentation The fragmentation pattern, i.e, The break up process of molecular ion into smaller ions, called fragment ions or daughter ions. The fragmentation of even simple molecules produces a large number of ions of different masses. A complex spectrum is obtained which often permits identification of compound or recognition of the presence of functional group in compounds. It should be noted that all fragments ions are not of equal significance in ascertaining the structure of the compound.

10. Fragmentation pattern of Isomeric pentane :

11. There are two important types of fragmentations: A neutral molecule such as H2O, CO, C2H4, HCl, HCN, etc. is eliminated. This loss of a neutral molecule gives a new fragment whose mass number has the same parity i.e., odd or evenness as the parent. Fragmentation parents may involve a seperation into the ion part and the radical part and this process channge the parity. The elimination of neutral fragments gives new radical cations, which are knows as odd electron fragments, while those formed by the elimination of a free radical are know as even electron fragments. This rule is of great significance in deciding the mode of fragmentation. The loss of and alkene fragment by a cyclic rearrangement of a carbonyl compound with γ- hydrogen s is known as mclafferty rearrangement.

12. Mclafferty Rearrangement It is a very is a very common fragmentation reaction observed in a mass spectrometry. This fragmentation was first described by Fred Mclafferty in 1956. For maclafferty reaction molecule must contain at least on gamma hydrogen and the functionality which can form radical cation. general structure of molecule Z=C, N,O

13. It involve cleavage of a α – β b ond followed by transfer of γ – H atom. This rearrangement leads to the elimination of neutral atom like,

14. Reaction

15. Maclafferty rearrangement Reaction mechanism :

16. referance Books : Spectroscopy – H. Kaur Spectrocopy of organic compounds – P.S. Kalsi Spectroscopy- B.K. Sharma

17. Thank you