RichardZhang

Borane

Optimization of Borane(3-21G)

Optimization of Borane(6-31G)

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BH3

Vibrational Information

Mode	Vibration	Intensity	Symmetry	IR Active	Type
1	1163	93	A2'	Yes	out-of-plane bend
2	1213	14	E'	Yes	bend
3	1213	14	E'	Yes	bend
4	2582	0	A1'	No	symmetric stretch
5	2715	126	E'	Yes	asymmetric stretch
6	2715	126	E'	Yes	asymmetric stretch

The IR spectrum of Ammonia borane

There are less than six peaks in the spectrum even though there are obvious six vibrations. This is because the translation modes are degenerate each other, such as mode 2 and mod 3, mode 5 and mode 6. In addition, the vibration mode 4 is IR inactive, which therefore also missed in the IR spectrum.

The molecular orbital of Borane

No obvious differences can be observed between the real and LCAO MOs, which means that the qualitative MO theory is quite accurate.

Association energy calculation

Optimization of Ammonia(6-31G)

1.RB3LYP/6-31G:

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Ammonia

Vibrational Information

Mode	Vibration	Intensity	Symmetry	IR Active	Type
1	1694	145	A	Yes	out-of-plane bend
2	1694	13	E	Yes	bend
3	1694	13	E	Yes	bend
4	3461	1	A1	No	symmetric stretch
5	3589	0	E	No	asymmetric stretch
6	3589	0	E	No	asymmetric stretch

The IR spectrum of Ammonia

Optimization of Ammonia Borane(6-31G)

1.RB3LYP/6-31G:

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Ammonia Borane

Calculation process

E(NH3)=-56.55776863 a.u ≈ -1.48492x10^5 kJ/mol

E(BH3)=-26.61532360 a.u ≈ -6.9879x10^4 kJ/mol

E(NH3BH3)=-83.22469012 a.u ≈ -2.18506x10^5 kJ/mol

ΔE = E(NH3BH3)-[E(BH3)+E(NH3)] = -2.18506x10^5+(6.9879x10^4+1.48492x10^5) ≈ -135 kJ/mol

The value of association energy is a negative value, which means the B-N dative bond is stronger than the ?

Borone tribromide

Optimization of borone tribromide(GEN)

1. RB3LYP/GEN:

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Boron tribromide

Vibrational Information

Mode	Vibration	Intensity	Symmetry	IR Active	Type
1	156	145	E'	NO	asymmetric stretch
2	156	13	E'	NO	asymmetric stretch
3	268	13	A1'	NO	symmetric stretch
4	378	1	A2	Yes	out-of-plane bend
5	763	0	E'	Yes	bend
6	763	0	E'	Yes	bend

The IR spectrum of Borone tribromide

The pps-optimisation of BBr3: DOI:10042/202437

The pps-frequency of BBr3: DOI:10042/202439

Project of aromaticity

Optimization of Benzene

1.RB3YLP/6-31G:

The optimisation file is linked to here

Benzene

The IR spectrum of Benzene

Optimization of Borazine

1.RB3YLP/6-31G:

The optimisation file is linked to here

Borazine

The IR spectrum of Borazine

The Natural Bond Orbital analysis

The charge diagram of Benzene

The charge diagram of Borazine

The atoms in benzene

Atom	Charge/a.u	Electronegativity
c	-0.239	2.5
H	0.239	2.2

The atoms in borazine

Atom	Charge/a.u	Electronegativity
B	0.747	2.0
N	-1.102	3.04
H-N	0.432	2.2
H-B	-0.077	2.2

According to the diagrams and tables shown above, it is obvious that the charge density in the benzene is evenly distributed. In addition, the charge of the hydrogen is 0.239 a.u and the charge of the carbon is -0.239, which is a big difference. This is mainly because of the electronegativity difference between H(2.2) and C(2.5). As carbon is more electronegative than hydrogen, it will attracts the charges toward itself, which therefore becomes more negative in charge density than hydrogen. For borazine, the distribution of charge density is more complex. The nitrogen is a strong electron withdrawing group as the electronegativity of N is around 3.04 which is much larger than the electronegativity of hydrogen(2.2)and boron(2.0). Therefore, it will pulls the charge density towards itself and away from the boron and hydrogen.

The MOs of Benzene and Borazine

MOs of Benzene	MOs of Borazine	Describtion
		These Molecular orbitals are MO no.14 for benzene and MO no.15 for Borazine. Both orbitals are the anti-bonding sigma orbitals. The orbital energy of benzene is -0.43854, which is almost the same as the energy of borazine(-0.43197). Based on the diagram, it is clear that the molecular orbital of benzene is more symmetric than that of borazine. This is because the
		Both orbitals are the no.21 MOs in benzene and borazine and they are both anti-bonding pi orbitals. The MO of benzene is more symmeric than the MO of borazine. The energy of benzene orbital is -0.24691, which is less negative than the energy of borazine(-0.2759). Moreover, it is clear to see that the upper portion of MO in the borazine is smaller than the lower part. This is because the higher electronegativity nitrogens withdraw the charge density toward their part.
		Both orbitals are the no.24 MOs in benzene and borazine and they are both bonding sigma orbitals. The orbital energy of benzene is 0.09117 and the orbital energy of borazine is 0.08953. The MO of benzene is more symmetric than that of borazine. This is because the large electronegativity of nitrogens withdraw electron density from hydrogen and boron and distored the structure of the molecular orbital.

The aromaticity is applied in the organic chemistry to descirbe a cyclic, flat molecule with a ring of resonance bonds. These bonds induces more stability other types of structure or arrangements of atoms. In terms of the electronic nature of the molecule, aromaticity describes a conjugated system often made of alternating single and double bonds in a ring. This configuration allows for the electrons in the molecule's pi system to be delocalized around the ring, increasing the molecule's stability.