Structure and Reactivity | Organic Chemistry 1

Structure and reactivity in organic chemistry are studied in this chapter: 3 classes of reagents (Bronsted acids/bases, Lewis acids/bases, nucleophiles/electrophiles), chemical functional groups, naming of alkanes (an example of naming in organic chemistry), introduction to isomerism

Bronsted Acids/Bases

A Bronsted acid is a proton donor
A Bronsted base is a proton acceptor

 

 


The more stable a base, the weaker the base and the stronger the conjugate acid

Effects which affect the stability and therefore the strength of acid and base:

- Resonance forms: the more forms a chemical compound has, the more stable it is
- Hybridization effect: lone pairs of electrons are stabilized by the s character of orbital. The % of s character is 25% in sp3 hybridization, 33% in sp2 and 50% in sp. Therefore, increasing basicity correlates with hybridization as follows: sp < sp2 < sp3​​​​​​​
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- Inductive effect: bases are stabilized by electron-withdrawing inductive effect (-I effect)

 

Lewis Acids/Bases

A Lewis acid is a substance that accepts an electron pair
A Lewis base is a substance that donates an electron pair

 

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Nucleophile vs. Electrophile

Nucleophile: an electron-rich species that can form a covalent bond by donating an electron pair to an electron-poor atom. Nucleophiles can be neutral or negatively charged. These are also Lewis bases
 

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Electrophile: an electron-poor species that can form a covalent bond by accepting an electron pair from a nucleophile. Electrophiles can be either neutral or positively charged. These are also Lewis acids
 

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Functional Groups

A functional group is a group of atoms that has a characteristic chemical behavior

 

Carbonyl Group (Compound with a C=O bond):

Naming Alkanes

Alkanes:

Organic compounds consisting entirely of C-C and C-H single bonds (saturated hydrocarbons)
General formula: CnH2n+2

 

Straight-chain alkanes:

CH4 = methane
CH3CH3 = C2H= ethane
CH3CH2CH3 = C3H8 = propane
C4H10 = butane
C5H12 = pentane
C6H14 = hexane
C7H16 = heptane
C8H18 = octane
C9H20 = nonane
C10H22 = decane

If an H is removed from an alkane, the partial structure is called alkyl and is part of larger compounds. To name them, we replace the suffix 'ane' by 'yl'

 

CH3- = methyl
CH3CH2- = ethyl
CH3CH2CH2- = propyl

 

Some other common substituents:

 

Naming: 

Prefix-Parent-ane 
Prefix = Substituents, Parent = Longest chain of C atoms, -ane = alkane chemical function

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1) Find the longest continuous chain of carbon atoms. If a molecule has two chains of equal length, choose the chain with the greatest number of substituents
2) Name all groups attached to the longest chain as alkyl substituents
3) Number the carbon atoms in the longest chain starting with the end closest to a substituent. If there are 2 subst. at equal distance: lower number for the first subst. in alphabetical order. If the 2 subst. are the same, check the 3rd one
4) Write the name as a single word, using hyphens to separate different prefixes and commas to separate numbers. Cite the subst. in alphabetical order (di, tri, tetra ... not counted)

 

1) Longest chain: 7 carbon atoms ⇒ heptane
2) 2 methyl substituents + 1 ethyl substituent
3) The right end is the closest to a subst.: number the C atoms from the right to the left
4) 4-ethyl-3,3-dimethylheptane

Isomers vs. Conformers

Constitutional isomers: chemical species with the same molecular formula but different connectivity
 

 

Conformers (or conformational isomers): specific arrangements of atoms of the same molecule resulting from a rotation around a single bond
 

Newman Projection of 2 conformers of 1,2-dichloroethane resulting from a rotation around the C-C single bond