![\"\"](\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-80.png\" "\\"\\"")
<\/figure><\/div>\n\n\n\nClassification of Carbocation<\/h2>\n\n\n\n
A\ncarbocation is classified into three basic categories<\/p>\n\n\n\n
- Primary\ncarbocation<\/li>
- Secondary\ncarbocation<\/li>
- Tertiary\ncarbocation<\/li><\/ol>\n\n\n\n
- Primary carbocations<\/strong><\/li><\/ul>\n\n\n\n
In a\nprimary carbocation, the positive charge which is carried by carbon is only\nattached to one other alkyl group.<\/p>\n\n\n\n
By using the symbol R for an alkyl group, a primary carbocation can be written as follows<\/p>\n\n\n\n
![\"\"](\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-81.png\" "\\"\\"")
<\/figure><\/div>\n\n\n\nFew examples of primary carbocation are given below:<\/p>\n\n\n\n
![\"\"](\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-82.png\" "\\"\\"")
<\/figure><\/div>\n\n\n\nObserve\nthat it doesn’t matter how complicates the attached alkyl group is you just\nneed to count the number of bonds from the positive carbon to other carbon\natoms. In the examples given above, there is only one such link.<\/p>\n\n\n\n
- Secondary carbocation<\/strong><\/li><\/ul>\n\n\n\n
In a\nsecondary carbocation, the positively charged carbon is attached to two other\nalkyl groups, which may be different or the same.<\/p>\n\n\n\n
The general formula of a secondary carbocation can be written as given below, where R and R\u2019 indicates the alkyl groups which may be the same or different.<\/p>\n\n\n\n
![\"\"](\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-83.png\" "\\"\\"")
<\/figure><\/div>\n\n\n\nFew examples of secondary carbocation are given below:<\/p>\n\n\n\n
![\"\"](\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-84.png\" "\\"\\"")
<\/figure><\/div>\n\n\n\n- Tertiary carbocation<\/strong><\/li><\/ul>\n\n\n\n
In a\ntertiary carbocation, the positively charged carbon is attached to three alkyl\ngroups, which may be any combination of the same or different.<\/p>\n\n\n\n
A general formula of tertiary carbonation is given below where R, R\u2019 and R\u201d are alkyl groups and it may be different or same.<\/p>\n\n\n\n
![\"\"](\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-85.png\" "\\"\\"")
<\/figure><\/div>\n\n\n\nFew examples of tertiary carbonation are given below<\/p>\n\n\n\n
![\"\"](\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-86.png\" "\\"\\"")
<\/figure><\/div>\n\n\n\nTertiary Carbocation stability<\/h2>\n\n\n\n
Generally, Carbocations are unstable and relatively hard to form. Usually, they can’t be isolated from a reaction as they immediately react to fill their empty p orbital. As they are electron deficient so when the attaching electron donates groups like alkyl groups, the carbonation will help to stabilize the carbonation. General stability order shows very clearly that tertiary carbocation is the most stable among all, as it is surrounded by three other carbon atoms that share the burden of its positive charge.<\/p>\n\n\n\n
The electron pushing effect of alkyl groups<\/h2>\n\n\n\n
Maybe\nyou are familiar with an idea that bromine is more electronegative than that of\nhydrogen, therefore in the H-Br bond, the electrons are grasped closer to the\nbromine than the hydrogen. a bromine atom which is attached to a carbon atom\nwould have exactly the same effect- the electrons being pulled towards the\nbromine end of the bond. the bromine has a negative inductive effect.<\/p>\n\n\n\n
The\nalkyl group will act exactly the opposite and rather than drawing electrons\ntowards themselves, they tend to push electrons away. This means that the alkyl\ngroup becomes slightly positive and the carbon to which they are attached\nbecomes slightly negative. So the alkyl group will have a positive inductive\neffect.<\/p>\n\n\n\n
This is occasionally shown as, for example<\/p>\n\n\n\n
![\"\"](\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-87.png\" "\\"\\"")
<\/figure><\/div>\n\n\n\nThe\narrow indicates that the electrons are being pushed away from the CH3<\/sub>\ngroup. The plus sign on the left-hand end of it indicates that the CH3 group is\nbecoming positive. The symbols \u03b4+ and \u03b4- simply support that idea.<\/p>\n\n\n\n
The\nimportance of spreading charge around in making ions stable<\/p>\n\n\n\n
According\nto a rule-of-thumb if a charge is too localized (all concentrated on one atom)\nthe ion will be much stable than if the charge is spread out over several\natoms.<\/p>\n\n\n\n
Applying that to carbocations of all three kinds<\/p>\n\n\n\n
![\"\"](\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-88.png\" "\\"\\"")
<\/figure><\/div>\n\n\n\nYou\nwill notice that the electron pushing effect of the CH3 group is to put a more\nand more negative charge on the positive carbon as we move from primary to\nsecondary to tertiary carbocations. This effect is obviously to cut down that\npositive charge.<\/p>\n\n\n\n
At the\nsame time, the area that is around the various CH3 groups is becoming somewhat\npositive. Then the net effect is that the positive charge is spread out over\nmore and more atoms as we move from primary to secondary to tertiary ions.<\/p>\n\n\n\n
The\nmore we spread the charge around, the more stable the ion becomes.<\/p>\n\n\n\n
The stability of tertiary carbocation in term of energy<\/h2>\n\n\n\n
If we\ntalk about secondary carbocations being more stable than primary ones, what\nexactly do we mean? Here, we are actually talking about the energetic\nstability-in energy ladder which is given below shows that the secondary\ncarbocations are lower in the energy ladder than the primary ones.<\/p>\n\n\n\n
It\nmeans more energy is required to make primary carbocation than a secondary one.\nIf we have a choice between making a secondary ion or primary one, definitely\nto make secondary carbocations will be much easier.<\/p>\n\n\n\n
Similarly,\nin an energy ladder, tertiary carbocation is lower than secondary ones, so\nsecondary carbocations will require more energy to form than tertiary\ncarbocations. If we will be given a choice of making a tertiary or secondary\none, we will definitely go for tertiary carbocations.<\/p>\n\n\n\n
This\nhas important implications in the reactions of unsymmetrical alkenes.<\/p>\n\n\n\n
Factors that stabilize tertiary carbocations<\/h2>\n\n\n\n
There\nare three main factors that increase the stability of tertiary carbocations<\/p>\n\n\n\n
- By\nincreasing the number of adjacent carbon atom: methyl is the least stable\ncarbocation <primary<secondary<tertiary (the most stable carbocation).<\/li>
- The\nadjacent pi bonds which allow the p-orbital carbocation to be a part of a conjugated\npi-system (delocalization through resonance)<\/li>
- Adjacent\natoms with lone pairs<\/li><\/ul>\n\n\n\n
References<\/h4>\n\n\n\n
- https:\/\/www.masterorganicchemistry.com\/2011\/03\/11\/3-factors-that-stabilize-carbocations\/<\/a><\/li>
- http:\/\/www.chem.ucla.edu\/~harding\/tutorials\/cc.pdf<\/a><\/li>
- https:\/\/www.chemguide.co.uk\/mechanisms\/eladd\/carbonium.html<\/a><\/li><\/ul>\n","protected":false},"excerpt":{"rendered":"
INTRODUCTION What is carbocation? A carbocation is a molecule that has a carbon atom that bears three bonds and a positive formal charge. Generally, the carbocations are unstable because they do not have eight electrons that satisfy the octet rule. Classification of Carbocation A carbocation is classified into three basic categories Primary carbocation Secondary carbocation … Read more<\/a><\/p>\n","protected":false},"author":6,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"rating_form_position":"","rating_results_position":"","mr_structured_data_type":""},"categories":[55],"tags":[],"multi-rating":{"mr_rating_results":[{"adjusted_star_result":5,"star_result":5,"total_max_option_value":5,"adjusted_score_result":5,"score_result":5,"percentage_result":100,"adjusted_percentage_result":100,"count":1,"post_id":1243}]},"_links":{"self":[{"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/posts\/1243"}],"collection":[{"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/users\/6"}],"replies":[{"embeddable":true,"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/comments?post=1243"}],"version-history":[{"count":6,"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/posts\/1243\/revisions"}],"predecessor-version":[{"id":1326,"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/posts\/1243\/revisions\/1326"}],"wp:attachment":[{"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/media?parent=1243"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/categories?post=1243"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/tags?post=1243"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
- http:\/\/www.chem.ucla.edu\/~harding\/tutorials\/cc.pdf<\/a><\/li>
- https:\/\/www.masterorganicchemistry.com\/2011\/03\/11\/3-factors-that-stabilize-carbocations\/<\/a><\/li>
- Tertiary carbocation<\/strong><\/li><\/ul>\n\n\n\n
- Secondary carbocation<\/strong><\/li><\/ul>\n\n\n\n
- Primary carbocations<\/strong><\/li><\/ul>\n\n\n\n