What is an Atom?

It is the story of an atom. Atom is just like us. As you know, in this universe everything has one counterpart like day-night, good-bad, hot-cold, plus-minus and so on. Atom also has positive and negative parts. Its positive part is called proton and its counter companion is electron which is negative. They are always present in equal number to maintain the neutrality of an atom. As you can understand they cannot stay together. Both have their unique character. Electrons are quite restless and full of energy unlike protons. So protons choose to go in the core/nucleus of an atom and rest there. While electrons prefer to continually revolve around the nucleus. Yes, just like planets in our solar system revolve around the Sun. You know every planet has its own track in which it moves around the Sun. Electrons also have their tracks and each track has its particular energy level. Just imagine electrons are moving in a circular racing track with the nucleus at its centre. Inner tracks are closer to the nucleus and smaller than others. They are occupied by less energy electrons. As the distance between nucleus and tracks increases, energy level of tracks increases and so does the energy of electrons belonging to them.

How do electrons move around? Do they run or jump or walk? An electron's motion is like our Earth. Just like the Earth, it revolves around its axis and simultaneously moves in its track. You can also compare it with your childhood toy “spin top”. Every electron revolves clockwise or anticlockwise in its axis while it travels in the track.

How many electrons can run in a particular track? Every track allows a particular number of electrons to run. Track 1 which is closest to the nucleus allows only 2electrons. Track 2 allows 8 electrons, track 3 also allows 18 and track 4 allows 32.

Do electrons have some vehicle or anything like that? Yes they have. As you know, everyone can afford a different car according to their status. You can imagine that Electrons travel in different models of spaceships. These spaceships are provided to them according to their energy level or in other words according to the  track in which they are moving. Every spaceship has a different occupancy and shape. Spaceship for the electrons moving in track 1 have “s” model of spaceship. This model is spherical in shape and has only one compartment with 2 seats. Spaceship for the electrons moving in track 2 have two models of spaceship “s” and “p” model. Model “p” is dumbbell  shaped and has three compartments, each of which has 2 seats. Spaceship for the electrons moving in track 3 have three models of spaceship “s”, “p” and “d” model. Model “d” is double-dumbbell shaped and has five compartments, each of which has 2 seats. Spaceship for the electrons moving in track 4 have four models of spaceship “s”, “p”, “d” and “f” model. Model “f” is the most superior one and it has a very complex shape and has seven compartments, each of which has 2 seats.

 

Now you can imagine protons are staying inside the nucleus and electrons are roaming around it in the tracks. Electron looks like your “spinning top” which is travelling in its spaceship.

You may wonder how all protons gently stay in the nucleus. They all have positive charge they must repel each other like same magnetic poles do. Yes they repel each other, but for the harmony the peace maker neutrons are present inside the nucleus. They are neutral in charge so they keep protons at a safe distance.

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Fragmentation and mass spectra of Esters

• Molecular ion peak is weak but noticeable.
• The most characteristic peak results from McLafferty rearrangement. 
  
• Other important Peaks results from bond cleavage next to C=O.
  
• gives an easily recognizable peak for esters.
• Easters, in which the acid portion is the predominant portion of molecule, the fragmentation pattern is same as described for the fragmentation pattern of free acid.
  
• Easters, in which the alcohol portion is the predominant portion of molecule, eliminate a molecule of acid on fragmentation.
• lets check spectrum of methyl octanoate
  

Fragmentation and mass spectra of Aliphatic Acids

• Molecular ion peak is weak but noticeable.
• In short chain acids, cleavage of bonds next to C=O results prominent peaks at M-OH and M-CO₂H.
• In long chain acids, the spectrum consists of two series of peaks resulting from cleavage at each C-C bond with retention of charge either on the Oxygen containing fragment or the alkyl containing fragment.
• The most characteristic peak is m/z 60 resulting from the McLafferty rearrangement. Branching at α carbon enhance this cleavage.
  

lets examine spectrum of decanoic acid 

Fragmentation and mass spectra of Aldehydes

• Molecular ion peak is very weak.
• M-1 peak is good diagnostic peak, even for long chain Aldehyde.
• In lower aldehydes, α-cleavage is prominent with retention of charge on oxygen.
• In straight chain Aldehydes, the other diagnostic peaks are at 

1. M-18 because loss of water
2. M-28 because loss of ethylene
3. M-43 because loss of CH2=CH-O
4. M-44 because loss of CH2=CH-OH

Fragmentation and mass spectra of Ketone

• The mass spectrum of a ketone generally has an intense molecular ion peak.
• Ketones fragment homolytically at the C-C bond adjacent to the C=O bond, which results in the formation of a cation with a positive charge shared by two atoms. The alkyl group leading to the more stable radical is the one that is more easily cleaved.

• If one of the alkyl groups attached to the carbonyl carbon has γ hydrogen, a cleavage known as a McLafferty rearrangement may occur.
  

lets interpret this spectrum

Fragmentation and mass spectra of Ethers

• Molecular ion peak is small.
• The presence of oxygen atom can be deduced from strong peaks at m/z31,45,59,73 ect. These peaks represents the RO⁺ and ROCH₂⁺fragments.
• Fragmentation of the resulting molecular ion occurs in two principal ways:

1. A C-O bond is cleaved heterolytically, with the electrons going to the more electronegative oxygen atom. 
   
2. A C-C bond is cleaved homolytically at the position because it leads to a relatively stable cation in which the positive charge is shared by two atoms (carbon and oxygen).
   

Now try to this interpret spectrum

Fragmentation pattern and mass spectra of Alcohols

·        Molecular ion peak of primary and secondary alcohol is quite small and for tertiary alcohol is undetectable.

·        Molecular ion peak is formed by the removal of one electron from the lone pairs on the oxygen atom of primary and secondary alcohol.

·        Cleavage of C-C bond next to the oxygen (α cleavage) is of general occurrence.

o   Thus primary alcohol  show a prominent peak resulting from oxoniumion (m/z 31)

o   secondary alcohol show a prominent peak resulting from (m/z 45,59,73 etc)

o   tertiary alcohol show a prominent peak resulting from(m/z 59, 73, 87 etc)

·     A distinct and sometimes prominent peak can usually be found at M-18 from loss of H₂O.

·     In primary alcohol elimination of water, together with elimination of alkene, accounts for the presence of a peak at M-(alkene+ H₂O) ie (m/z 46, 74, 102 etc)

lets examine spectrum of 1-pentanol

examine spectrum of  secondary alc. 2-pentanol

now examine spectrum of  tertiary alc. 2-methyl-2-butanol

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