Question

Natural Bond Orbitals

Natural Bond Orbitals (NBOs) convert molecular orbitals to the form of localised bonding orbitals that correspond to Lewis structures. Natural bond orbitals attempt to provide the most accurate natural Lewis structure. The NBOs are localised and are thus different to MOs - it is important not to over-interpret NBOs - NBOs give an indication of bonding and electronic structure in the framework of Lewis structures.

In this exercise you will explore the bonding description of methanol from NBO calculations.

Perform a geometry optimization + frequency calculation on methanol at the B3LYP/6-31G(d) level of theory. Using this optimized geometry perform a Natural Bond Orbital calculation at the same level of theory. Once the calculation is complete use the data to answer the following questions.

Natural Bond Orbitals

NBO calculations identify orbitals as core (CR), bonding (BD), or lone-pairs (LP). Unoccupied NBOs are indicated with an asterisk. The bonding NBOs and lone-pairs enable you to construct a Lewis structure to describe the bonding in a molecule.   

The number of Core-Type (CR) Natural Bonding Orbitals in methanol is (..............)The Core-Type NBOs reside on (...........) (Oxygen only, carbon only, Oxygen + Carbon OR sp3 hybrids) and correspond to (...............) ( sp3,sp2, 2s, 2p OR 1s) orbitals.

The number of Bonding-Type (BD) Natural Bonding Orbitals in methanol is (…………..). There are (………..) bonding orbitals from the C atom in methanol.

The number of Lone Pair-Type (LP) Natural Bonding Orbitals in methanol is (………..). The Lone-Pair-Type NBOs reside on (………….) (Oxygen only, carbon only, Oxygen + Carbon OR sp3 hybrids).  

Natural Hybrid Orbitals

An NBO calculation also produces Natural Hybrid Orbitals (NHO) from the Natural Atomic Orbitals (NAO).

The lone pair NBOs are made up from Natural Hybrid Orbitals (NHO). Identify which NHOs make up the first lone pair, LP(1), and view the NHO in the data-viewer by selecting the appropriate NHO. LP(1) resides on the AnswerCarbonHydrogenOxygen atom and has 51.12% (…………) ( P, LP, BD,CR,F,RY,S or G) character, and 48.82% (…………)(D,B,DG,LP,RY,CR,F or S )character. This LP NHO can be best described as an sp(………..) hybrid orbital (give a number to 2 decimal places).

Identify which NHOs make up the second lone pair, LP(2), and view the NHO in the data-viewer by selecting the NHO. LP(2) resides on the (………..) (Oxygen,Carbon or Hydrogen) atom and has 0.00% (…………) (G,DF,P,RY,BD,LP,CR or S) character, and 99.90% (……….) (F,L,PC,R,G,D,BD,P,S or RY) character. This LP NHO can be best described a (…………) (D Orbitalsp, Hybrid Orbital, sp2 Hybrid Orbital, sp3 Hybrid Orbital, P Orbital or S Orbital).

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I did not get any calculations

Can you find answers? please

Answer 1

Natural bond orbitals:-

1) Core type (CR) natural Bonding orbitals in methanol is 2 .

2)The core type NBOs reside on Carbon+Oxygen.

3)core type NBOs correspond to 2s orbitals.

4)The number of bonding type (BD) natural Bonding orbitals in methanol is 5. I.e Three C-H,one C-0 and one O-H.

5)There are Four bonding orbitals from the C-atom in methanol i.e one C-O and three C-H.

6)The number of lone pair type(LP) natural Bonding orbitals in methanol is two.

7) The lone pair type of NBOs reside on Oxygen only.