Бензол құрылымы және тұрақтылық. Химия, 11 сынып, презентация.

Тұрақтылыққа арналған термодинамикалық дәлел

Қанықпаған көмірсутектер тиісті қаныққан қосылысқа азайтылған кезде энергия шығады. Бір мольге бөлінетін жылу мөлшерін өлшеуге болады (гидрогенизация энтальпия).

Тұрақтылыққа арналған термодинамикалық дәлел

2

3

- 120 kJ mol-1

Циклогексен (бір С = С байланысы) циклогексанға дейін азайғанда, бір мольге 120 кДж энергия бөлінеді.

C6H10(l) + H2(g) ——> C6H12(l)

Қанықпаған көмірсутектер тиісті қаныққан қосылысқа азайтылған кезде энергия шығады. Бір мольге бөлінетін жылу мөлшерін өлшеуге болады (гидрогенизация энтальпия).

Тұрақтылыққа арналған термодинамикалық дәлел

2

3

- 120 kJ mol-1

Theoretical

- 360 kJ mol-1

(3 x -120)

Циклогексен (бір С = С байланысы) циклогексанға дейін азайғанда, бір мольге 120 кДж энергия бөлінеді.

C6H10(l) + H2(g) ——> C6H12(l)

Теориялық тұрғыдан, егер бензолда үш бөлек C = C байланысы болса, онда циклогексанға азайған кезде әр меңге 360 кДж бөлінеді.

C6H6(l) + 3H2(g) ——> C6H12(l)

Қанықпаған көмірсутектер тиісті қаныққан қосылысқа азайтылған кезде энергия шығады. Бір мольге бөлінетін жылу мөлшерін өлшеуге болады (гидрогенизация энтальпия).

Тұрақтылыққа арналған термодинамикалық дәлел

2

3

Experimental

- 208 kJ mol-1

- 120 kJ mol-1

Theoretical

- 360 kJ mol-1

(3 x -120)

Циклогексен (бір С = С байланысы) циклогексанға дейін азайғанда, бір мольге 120 кДж энергия бөлінеді.

C6H10(l) + H2(g) ——> C6H12(l)

Теориялық тұрғыдан, егер бензолда үш бөлек C = C байланысы болса, онда циклогексанға азайған кезде әр меңге 360 кДж бөлінеді.

C6H6(l) + 3H2(g) ——> C6H12(l)

Нақты бензол бір мольге тек 208 кДж шығарады, бұл энергия шкаласын төмендетеді

Қанықпаған көмірсутектер тиісті қаныққан қосылысқа азайтылған кезде энергия шығады. Бір мольге бөлінетін жылу мөлшерін өлшеуге болады (гидрогенизация энтальпия).

THERMODYNAMIC EVIDENCE FOR STABILITY

2

3

MORE STABLE THAN EXPECTED

by 152 kJ mol-1

Experimental

- 208 kJ mol-1

- 120 kJ mol-1

Theoretical

- 360 kJ mol-1

(3 x -120)

When cyclohexene (one C=C bond) is reduced to cyclohexane, 120kJ of energy is released per mole.

C6H10(l) + H2(g) ——> C6H12(l)

Theoretically, if benzene contained three separate C=C bonds it would release 360kJ per mole when reduced to cyclohexane

C6H6(l) + 3H2(g) ——> C6H12(l)

Actual benzene releases only 208kJ per mole when reduced, putting it lower down the energy scale

It is 152kJ per mole more stable than expected.

This value is known as the RESONANCE ENERGY.

When unsaturated hydrocarbons are reduced to the corresponding saturated compound, energy is released. The amount of heat liberated per mole (enthalpy of hydrogenation) can be measured.

THERMODYNAMIC EVIDENCE FOR STABILITY

2

3

MORE STABLE THAN EXPECTED

by 152 kJ mol-1

Experimental

- 208 kJ mol-1

- 120 kJ mol-1

Theoretical

- 360 kJ mol-1

(3 x -120)

When cyclohexene (one C=C bond) is reduced to cyclohexane, 120kJ of energy is released per mole.

C6H10(l) + H2(g) ——> C6H12(l)

Theoretically, if benzene contained three separate C=C bonds it would release 360kJ per mole when reduced to cyclohexane

C6H6(l) + 3H2(g) ——> C6H12(l)

Actual benzene releases only 208kJ per mole when reduced, putting it lower down the energy scale

It is 152kJ per mole more stable than expected.

This value is known as the RESONANCE ENERGY.

When unsaturated hydrocarbons are reduced to the corresponding saturated compound, energy is released. The amount of heat liberated per mole (enthalpy of hydrogenation) can be measured.

HYBRIDISATION OF ORBITALS - REVISION

The electronic configuration of a carbon atom is 1s22s22p2

HYBRIDISATION OF ORBITALS - REVISION

The electronic configuration of a carbon atom is 1s22s22p2

If you provide a bit of energy you can promote (lift) one of the s electrons into a p orbital. The configuration is now 1s22s12p3

The process is favourable because of the arrangement of electrons; four unpaired and with less repulsion is more stable

HYBRIDISATION OF ORBITALS - REVISION

The four orbitals (an s and three p’s) combine or HYBRIDISE to give four new orbitals. All four orbitals are equivalent.

2s22p2

2s12p3

4 x sp3

HYBRIDISE

sp3 HYBRIDISATION

HYBRIDISATION OF ORBITALS - REVISION

Alternatively, only three orbitals (an s and two p’s) combine or HYBRIDISE to give three new orbitals. All three orbitals are equivalent. The remaining 2p orbital is unchanged.

2s22p2

2s12p3

3 x sp2

2p

HYBRIDISE

sp2 HYBRIDISATION

In ALKANES, the four sp3 orbitals repel each other into a tetrahedral arrangement.

In ALKENES, the three sp2 orbitals repel each other into a planar arrangement and the 2p orbital lies at right angles to them

STRUCTURE OF ALKENES - REVISION

Covalent bonds are formed by overlap of orbitals.

An sp2 orbital from each carbon overlaps to form a single C-C bond.

The resulting bond is called a SIGMA (δ) bond.

STRUCTURE OF ALKENES - REVISION

The two 2p orbitals also overlap. This forms a second bond; it is known as a PI (π) bond.

For maximum overlap and hence the strongest bond, the 2p orbitals are in line.

This gives rise to the planar arrangement around C=C bonds.

STRUCTURE OF ALKENES - REVISION

two sp2 orbitals overlap to form a sigma bond between the two carbon atoms

ORBITAL OVERLAP IN ETHENE - REVIEW

two 2p orbitals overlap to form a pi bond between the two carbon atoms

s orbitals in hydrogen overlap with the sp2 orbitals in carbon to form C-H bonds

the resulting shape is planar with bond angles of 120º

STRUCTURE OF BENZENE - DELOCALISATION

The theory suggested that instead of three localised (in one position) double bonds,

the six p (p) electrons making up those bonds were delocalised (not in any one

particular position) around the ring by overlapping the p orbitals. There would be no

double bonds and all bond lengths would be equal. It also gave a planar structure.

6 single bonds

STRUCTURE OF BENZENE - DELOCALISATION

6 single bonds

one way to overlap

adjacent p orbitals

The theory suggested that instead of three localised (in one position) double bonds,

the six p (p) electrons making up those bonds were delocalised (not in any one

particular position) around the ring by overlapping the p orbitals. There would be no

double bonds and all bond lengths would be equal. It also gave a planar structure.

STRUCTURE OF BENZENE - DELOCALISATION

6 single bonds

one way to overlap

adjacent p orbitals

another

possibility

The theory suggested that instead of three localised (in one position) double bonds,

the six p (p) electrons making up those bonds were delocalised (not in any one

particular position) around the ring by overlapping the p orbitals. There would be no

double bonds and all bond lengths would be equal. It also gave a planar structure.

STRUCTURE OF BENZENE - DELOCALISATION

6 single bonds

one way to overlap

adjacent p orbitals

delocalised pi

orbital system

another

possibility

The theory suggested that instead of three localised (in one position) double bonds,

the six p (p) electrons making up those bonds were delocalised (not in any one

particular position) around the ring by overlapping the p orbitals. There would be no

double bonds and all bond lengths would be equal. It also gave a planar structure.

STRUCTURE OF BENZENE - DELOCALISATION

6 single bonds

one way to overlap

adjacent p orbitals

delocalised pi

orbital system

another

possibility

This final structure was particularly stable and

resisted attempts to break it down through normal

electrophilic addition. However, substitution of any

hydrogen atoms would not affect the delocalisation.

The theory suggested that instead of three localised (in one position) double bonds,

the six p (p) electrons making up those bonds were delocalised (not in any one

particular position) around the ring by overlapping the p orbitals. There would be no

double bonds and all bond lengths would be equal. It also gave a planar structure.

STRUCTURE OF BENZENE