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Summary UNIT 14
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- PEARSON (PEARSON)
Summary of 45 pages for the course UNIT 14B APPLICATIONS OF ORGANIC CHEMISTRY at PEARSON (ASSIGNMENTS)
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Unit 14: Application of Organic ChemistryB: Understand the reactions and properties of aromatic compounds
Benzene
Benzene consists of a kekulés model of C6H6. Among the benzene characteristics, its aromaticity is the
main reason for it being unreactive. The p-orbital delocalization carbo on the sp2 hybridized carbon
provides benzene aromatic qualities. Benzene(C6H6) is structured as a planar molecule consisting of six-
carbon ring atoms. Each consisting of a hydrogen atom bonded to it. The delocalized electrons are
present both above as well as below the ring plane. Benzene is known as a natural occurring substance
that is created by forest fires as well as volcanoes and is found in various animals as well as plants.
Benzene is also known as a major industrial chemical that is created from both oil as well as coal.
Additionally, benzene is one of the most organic as well as simplest aromatic hydrocarbons, and its parent
compounds consist of various important aromatic compounds. The compounds come up as a colorless
liquid in addition to a characteristic odor. This compound is normally used in polystyrene production.
They are known to be very toxic in nature as well as carcinogen. Bing exposed to it can lead to leukemia.
The arrangement of benzene is a trigonal planar geometry consisting of hybrid orbitals structured at an
angle of 120°C to one another in a plane, whereas the p orbitals are arranged at right angles to them.
The atoms are hydrogens in the benzene structure. In the benzene structure, the double bonds are
divided up by a single bond, this is why the arrangements are known to consist of conjugated double
bonds. Additionally, a circle is utilized as a symbol in the interior of the hexagon utilized to show the 6 pi
electrons. Benzene is classified as a hydrocarbon because of its chemical formula. A compound containing
only hydrogen as well as carbon atoms. The formula as well as the structure disclose benzene as a pure
aromatic hydrocarbon.
Hybridization/Delocalization
Benzene is composed of a hydrogen atom (1s1) as well as a carbon atom (1s2 2s2 2py1). Each carbon
atom must be attached with three other atoms, including one hydrogen as well as 2 carbons. There are
not enough unpaired electrons to be able to create the required amount of bonds, so one of the 2s2 pairs
up. It should further be promoted to an empty 2pz orbital.
,The electron is developed from the 2s orbital to the empty 2p orbital, forming 4 unpaired electrons, with
only a small energy gap between both the 2s as well as 2p orbitals. Additionally, the extra energy released
when these electrons are utilized for bonding more than offsets the initial input. The carbon atom is then
in an exited state. Each carbon only attaches to the three other atoms, so if a carbon atom's outer orbital
hybridizes before creating a bond, it only requires hybridizing the three orbitals instead of hybridizing all
the four orbitals. They also utilize Two of the 2s as well as the 2p electrons, however the 2p electrons are
left alone and unchanged.
The newly created orbitals are known as sp2 hybrid orbitals due to the fact they consist of one orbital as
well as 2 p orbitals that rearrange. Additionally, the 3 sp3 hybrid orbitals are replaced as far away apart in
planes 120°C from one another. The rest of the p-orbitals are structured perpendicular to them.
Each of the carbon atoms is shown. It is the exact same as Ethen. However, the difference in benzene is
that each of the carbon atoms is attached to two of the similar carbon atoms instead of attached to just
one. Each carbon atom utilizes a sp2 hybrid to create a sigma bond in addition to two other carbon atoms
as well as one hydrogen atom. Here the sigma bond is created, however the p-orbitals are left alone.
The p electron of each of the carbon atoms begins to overlap with the electrons on either side of it. This
extensive lateral begins to overlap forming a pi bon system distributed throughout the carbocycle.
Additionally, electron delocalization is when the electrons are no longer held only between two carbon
,atoms, however, are distributed throughout the ring. Six of the delocalized electrons enter two three
molecule orbitals each.
Here, the sigma bond is further represented by a simple line.
Additionally, the two rings on top as well as below the molecule plane
show the molecular orbitals. Two delocalized electrons may be located
anywhere within these rings. However, the other 4 delocalized
electrons are further consisting in two similar however not identical,
molecular orbitals.
Benzene is known as a planar regular hexagon consisting of bond angles of 120°C. There is no alternating
double as well as single bonds due to the electron delocalization. The reason why it is a planar is due to
the fact it only then that the p orbitals may overlap latterly to be able to obtain a delocalized pi system.
The more they are delocalized, the more the electrons are spread out all around. The benzene is around
150kJ mol-1 when the delocalized electrons are in place. Some of the delocalized electrons will be added
to be able to attach the new atoms in the ring, if atom to a benzene ring is added on. The circle in the
middle shows the delocalized electrons below.
Kekulé structure
Kekule was the first person to provide the benzene structure, C6H6. The carbons are positioned in a
hexogen structure, as well as suggested alternating single as well as double bonds in between them.
Hydrogen is boned to each carbon atom. This diagram is normally simplified by omitting all the carbon as
well as hydrogen atoms. The diagram consists of a carbon atom at each corner. To figure out how many
hydrogen atoms are bonded to it, the bonds need to be counted away from each of the carbon atoms.
Here, each of the carbons consists of three bonds that are left. Additionally, carbon atom creates 4
bonds, which means it is missing one of the bonds as well as needs to be bonded to a hydrogen atom.
, Kekule structure was a good attempt, however it did have issues with it. Benzene might be expected to
react like ethene reacts due to the three double bonds. Additionally, ethene undergoes an addition
reaction where out of the two bonds, one of them connecting the carbon atoms is broken as well as the
electron is utilized to bond with an additional atom. However, benzene barely does this, it normally
undergoes a substitution reaction where one of the hydrogens is restored with something else new.
Additionally, benzene is structured as a planar molecule, where all atoms lie in one place. Kekule
structure is similar. The issue is that the C-C single as well as double bonds consist of various lengths. This
includes C-C(0.154nm) and C=C(0.134nm). This further shows that if a hexagon consists of a kekule
structure with alternating long as well as short sides, it will be irregularly shaped. All bonds in real
benzene are shown the same-length between both C-C as well as C=C at 0.139nm. The real benzene is
structured as a regular hexagon. Overall, the real benzene is much more stable compared to the
structure of kekule suggest. Every thermochemical calculation related to the kekule structure introduces
an error of around 150kJ mol-1. This is further demonstrated easily when using the enthalpy change of
hydrogeneration. Addition of hydrogen to something else is known as hydrogeneration. For instance,
when hydrogenation of ethene occurs its results in ethane.
CH2=CH2 + H2 —> CH3CH3
To create a fair comparison with benzene, the ring structure, it is therefore compared with cyclohexene.
Cyclohexene, which consists of the formula C6H10, consists of a 6-carbon ring consisting of only one C=C.
Cyclohexane, which consists of the formula C6H12, is created when hydrogen is added on. The CH group
is then a CH2 as well as the double bond is restored with a single bond. The cyclohexene as well as
cyclohexane structures are normally simplified by omitting all the carbons as well as the hydrogens, like
the structure kekule of benzene.
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