Write short note on Nucleophilic substitution in pyridine with examples
Answers
Explanation:
Nucleophilc substitution in pyridine favours not only position 2 but also position 4. In order to understand why, we must first draw out the intermediate structures and take a look at the different resonance stabilized forms that it have.
When the nucleophile is at the 2 and 4 position, the intermediate anion is stabilized by the electronegative nitrogen atom. This results in a more stable anion as compared to the intermediate anion when the the nucleophile is at the 3 position. Hence favouring the 2 and 4 position for nucleophilic substitution.
Why is pyridine more basic than aniline?
As Mark Foreman notes, the nitrogen lone pair in aniline is "tied up" in resonance, so that it is not as available to function as a base. This effect is large enough to drop the pKa of the NH2 group (the pKa of its conjugate acid) from around 10 (what we expect for saturated nitrogen) to about
Answer:
Pyridine is a basic heterocyclic organic compound with the chemical formula C
5H
5N. It is structurally related to benzene, with one methine group (=CH−) replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with a distinctive, unpleasant fish-like smell. Pyridine is colorless, but older or impure samples can appear yellow. The pyridine ring occurs in many important compounds, including agrochemicals, pharmaceuticals, and vitamins. Historically, pyridine was produced from coal tar. As of 2016, it is synthesized on the scale of about 20,000 tons per year worldwide.[2]
Pyridine
Full structural formula of pyridine
Skeletal formula of pyridine, showing the numbering convention
Ball-and-stick diagram of pyridine
Space-filling model of pyridine
Pyridine sample.jpg
Names
Preferred IUPAC name
Pyridine[1]
Systematic IUPAC name
Azabenzene
Other names
Azine
Azinine
1-Azacyclohexa-1,3,5-triene
Identifiers
CAS Number
110-86-1 check
3D model (JSmol)
Interactive image
ChEBI
CHEBI:16227 ☒
ChEMBL
ChEMBL266158 check
ChemSpider
1020 check
ECHA InfoCard
100.003.464 Edit this at Wikidata
EC Number
203-809-9
KEGG
C00747 check
PubChem CID
1049
UNII
NH9L3PP67S check
CompTox Dashboard (EPA)
DTXSID9021924 Edit this at Wikidata
InChI
InChI=1S/C5H5N/c1-2-4-6-5-3-1/h1-5H check
Key: JUJWROOIHBZHMG-UHFFFAOYSA-N check
InChI=1/C5H5N/c1-2-4-6-5-3-1/h1-5H
Key: JUJWROOIHBZHMG-UHFFFAOYAY
SMILES
c1ccncc1
Properties
Chemical formula
C5H5N
Molar mass
79.102 g·mol−1
Appearance
Colorless liquid[2]
Odor
Nauseating, fish-like[3]
Density
0.9819 g/mL[4]
Melting point
−41.6 °C (−42.9 °F; 231.6 K)
Boiling point
115.2 °C (239.4 °F; 388.3 K)
Solubility in water
Miscible
log P
0.73 [5]
Vapor pressure
16 mmHg (20 °C)[3]
Basicity (pKb)
8.77[6]
Conjugate acid
Pyridinium
Refractive index (nD)
1.5093
Viscosity
0.88 cP 25℃
Dipole moment
2.2 D[7]
Hazards[10]
Safety data sheet
See: data page
GHS pictograms
GHS02: FlammableGHS07: Harmful[8]
GHS Signal word
Danger
GHS hazard statements
H225, H302, H312, H332, H315, H319[8]
GHS precautionary statements
P210, P280, P301+312, P303+361+353, P304+340+312, P305+351+338[8]
NFPA 704 (fire diamond)
NFPA 704 four-colored diamond
230
Flash point
21 °C (70 °F; 294 K)
Explosive limits
1.8–12.4%[3]
Threshold limit value (TLV)
5 ppm (TWA)
Lethal dose or concentration (LD, LC):
LD50 (median dose)
891 mg/kg (rat, oral)
1500 mg/kg (mouse, oral)
1580 mg/kg (rat, oral)[9]
LC50 (median concentration)
9000 ppm (rat, 1 hr)[9]
NIOSH (US health exposure limits):
PEL (Permissible)
TWA 5 ppm (15 mg/m3)[3]
REL (Recommended)
TWA 5 ppm (15 mg/m3)[3]
IDLH (Immediate danger)
1000 ppm[3]
Related compounds
Related amines
Picoline
Quinoline
Related compounds
Aniline
Pyrimidine
Piperidine
Supplementary data page
Structure and
properties
Refractive index (n),
Dielectric constant (εr), etc.
Thermodynamic
data
Phase behaviour
solid–liquid–gas
Spectral data
UV, IR, NMR, MS
Explanation:
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