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Hi students welcome to this presentation in his presentation we will see some basic concept of aromaticity with simple explanation with examples the aromatic cupboards are called aromatics because of some distinctive smell they are processing some distinct smell actually they are derived from some hydrocarbons organic hormones actually without which life would
Not be possible on earth what are the characteristics of aromatic commerce actually there are the aromatica moles contains a set of commonly bound atoms with specific characteristics a delocalized a conjugated by system ah most commonly an arrangement of alternating single and double bonds actually they are processing the co-planar structures with the whole the
Contributing atoms in the same plane so by definitions the aromatic commands can be defined as unsaturated cycling molecules that process additional stability as a result of the arrangement of pi electrons associated with the unsaturation of the ring system so the robotic hormones can be also be known as arenas so the arrays are divided into some two categories
The first one is a carboxylic the copper cyclic means there is a ring containing only carbon atoms some aromatic compounds are heterocyclic that a ring contains at least one natural atoms other than carbon like nitrogen oxygen and sulfur so the aromatic hormones they are known as arenas ah they are classified as carboxylic and heterocyclic and the next one is
Hackles rule what is uncle’s rule actually in 1930 akkel showed that any a plane or cyclic molecules that containing a 2 6 10 14 and so on ah this number of pi electrons are associated with automatic characters actually there is a number of electrons the pi electrons numbers is very important there is a and the number is 2 6 10 14 and so on the presence will give
The aromatic character actually this represented by four and plus 2 where n is integer n is equal to zero one two three four etcetera so this four and plus two rule is known as the actors rule that gives the number of pilotons in the p orbital systems so you see that this rule uh the n that is given the n and i the number of the n value is a zero one two three four
Etcetera now the the number of pi electrons is given by four n plus two by electrons for if n c equal to zero say two electrons v n is equal to one six electrons and a two it is a ten pi electrons and three the number of electrons will be 14 and if n is equal to four the number of electrons will be eighteen so this circle is fully actually in order to be aromatic
The combo must be cycling with a p atomic orbital and all members of the ring and have four and plus 2 pi electrons the p orbital of the ring variance equal to zero one two three etcetera so the number of electrons will be 2 6 10 14 18 22 26 so in order to be aromatic a molecule must possess must be a cyclic planar completely conjugated compound with foreign
Plus two pi electrons ah considering aromaticity a commode can be classified in one of three ways so three ways we can distinguish the aromatic commerce the first one is a aromatic is a cyclic planar completely congeated compound with the four and plus two pi electrons and the aromatic a cyclic planar completely conjugated car mode with the foreign that lacks
One or more of the following requirements of aromaticity being cyclic planar and communicated any any of these characters is absent then it is the common mode is known as non aromatic actually you see there’s a an aromatic combo is more stable than similar aromatic acidic common having the same number of pilotrons you see the benzene is more stable because the the
Stability of a benzene because of the is a benzene is actually more stable because you see there’s a heats of hydrogenation would reflect the relatives thermodynamic stability of the carbons in practice actually you see the one three cyclo extra diene is slightly most durable than expected by about 2 kilo calories but you see the benzene hover is an extraordinary
36 kilo calorie per mole more stable than expected so there is a stability of a benzene and and then there is an anti-aromatic compound is less stable than acyclical mode having the same number of pi electrons the cyclobutodine is less stable than one three butadiene a compound that is not aromatic is similar in stability to an acyclic car mode having the same
Number of pilotrons 136 cyclo exception is similar in stability to cis cis2 for exide so it is not aromatic now according to the balance bone theory this the benzene molecule and other plane or aromatic hydrocarbon molecules or axonal rings of esp2 hybridized coronal atoms with unhybridized p orbital of each carbon atom perpendicular to the plane of the ring so
Now you see there are the first one is ah two pi electrons are present in this sp2 hybrides to our carbons and the second one there is no any pi electrons because all electrons the lone paratros are completely removed and the third one only one pi electron is present the fourth one two pi electrons are presented so the sv2 i position is very important ah feature
For the molecule to be a aromatic now you see that the benzene having the six pilotrons there is a harmonica mode the six p orbitals combine to give three bonding orbitals with the six pi electrons three antibonding with no electrons orbitals with the same energy or degenerate now these are foreign can be inscribed here a circle with an apex at the base and the
Horizontal lines are drawn at the points now you see a bone below there’s a below the center it’s a bonding orbital surface center the electrons are paired up and the above the center its antibonding orbitals a non-bonding orbital results when the polygon touches the circle at a horizontal diameter but here no such line is drawn because only there is no line
Which is passing through the diameter so there is no any non bonding electrons present only bonding and antibonding orbitals are present this is the molecular orbital diagram for benzene giving the bonding and the antibonding orbitals the next one is naphthalene and naphthalene is a 10 pi electrons which is also aromatic foreign plus two rule where n is equal
To 10 pi electrons ah three resonance forms and d localized electrons so by this representation you see there is a highly resonance structures giving a more stability for this naphthalene structure then aromatic ions aromatic ions now some examples we see is a cyclopropane actually cyclopropine is having one double bond but three out of three carbons two carbons
Are a speed to hybridize the carbon the third carbon is a sp3 carbon so this is a non planar and not aromatic it’s a not a aromatic common the cyclopropine but if it loses one hydride ion using one hydrated iron if we slot loss then it becomes cyclo propenyl cation cyclopropanyl cation now you see the all three carbons are sp2 hybridized and the planar ah and it’s
Actually the four n plus two where n equal to zero and equal to zero so the two pi electrons ah this is a very simplistic system because this exist is a very simplest as there is a smallest possible ring system with three member and the derived ancestor structure there is a cyclopropane actually the loss of hydro ion from this molecule leads to the cyclopropanyl
Cation which contains two pi electrons which contains two pi electrons distributed over the three carbon atoms of the panasonic cyclic system so these are an example for aromatic ions and another some other examples we see now the cyclopentadineal anion you see here it is a four and plus two variance equal to one six pi electrons a planar and all carbons are sp
To applies so there is a automatic amount and another example is a cyclohepto trinal cation where n is equal to one six pi here also the six pi electrons ah planar and all carbons are asp drivers and automatic so these are all some aromatic ions and there are some example for non aromatic you see the first one is ah sp2 sp2 sp3 ah so sp3 company is present so
The both and the second example is also having the sp3 carbon both are not aromatic both are non-armatic commodes you see here the first one is the non orbitic amount second one is anterior body because it’s a foreign which of the following are aromatic and the aromatic and non-aromatic the first one the common a you see a is anti-aromatic because it is a four
Pi electrons foreign rule actually is a foreign percent actually sp3 carbon percent is a non-oromatic whereas uh that carbon is a sp3 and the fourth one ah d is non automatic because here also the sp3 carbon present we have to see some other examples you see the first one the first one is not automatic because it does not obey hacker’s rule foreign actually n
Is equal to 1.5 so this is not a automatic amount the next one is also a not aromatic command because let’s not obey a console because n is equal to 0.5 and third one ah aromatic because n 0 0 cyclic planar a vehicle’s rule four n plus two is equal to two pi electrons n is equal to zero ah for this command this aromatic here also the n is equal to the number of
Pi electrons four and plus two rule number of electrons is ten and next is aromatic here also it is a 14 electrons so it will buy cycles rule so the value of n is equal to three and next one it is also not automatic because the eight pi electrons it doesn’t does not buy the cultural and this one is aromatic because the foreign concept of aromaticity so thank
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Transcribed from video
AROMATICITY- ORGANIC CHEMISTRY TOPIC-A CLEAR AND SIMPLE EXPLANATION ON AROMATICITY WITH EXAMPLES By UNIQUE CHEMISTRY – Professor SVS Academy
