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Related Concept Videos

SN1 Reaction: Stereochemistry02:15

SN1 Reaction: Stereochemistry

10.3K
This lesson provides an in-depth discussion of the stereochemical outcomes in an SN1 reaction.
In the first step of an SN1 reaction, the bond between the electrophilic carbon and the leaving group ionizes to generate the carbocation intermediate. The second step of the mechanism is the nucleophilic attack.
In the formed carbocation, the positively charged carbon is sp2 hybridized with a trigonal planar geometry. As all the three substituents lie on the same plane, a plane of symmetry for the...
10.3K
SN1 Reaction: Kinetics02:05

SN1 Reaction: Kinetics

9.6K
In an SN2 reaction, the reaction rate depends on both the type of nucleophile and the substrate. A hindered tertiary alkyl halide is practically inert to the SN2 mechanism despite using a strong nucleophile.
However, Sir Christopher Ingold and Edward D. Hughes, who studied the kinetics of various nucleophilic substitution reactions, noticed that a tertiary alkyl halide does undergo a nucleophilic substitution reaction in the presence of a weak nucleophile. While studying the substitution...
9.6K
SN1 Reaction: Mechanism02:25

SN1 Reaction: Mechanism

14.2K
Kinetic studies of ionization of a tertiary halide in a protic solvent suggest that only the substrate participates in the rate-determining step (slow step). The nucleophile is involved only after the slowest step. The SN1 reaction takes place in a multiple-step mechanism. 
Firstly, the haloalkane ionizes to generate a carbocation intermediate and a halide ion. This heterolytic cleavage is highly endothermic with large activation energy. The ionization of the substrate, facilitated by a...
14.2K
Acidity of 1-Alkynes02:42

Acidity of 1-Alkynes

11.2K

The acidic strength of hydrocarbons follows the order: Alkynes > Alkenes > Alkanes. The strength of an acid is commonly expressed in units of pKa — the lower the pKa, the stronger the acid. Among the hydrocarbons, terminal alkynes have lower pKa values and are, therefore, more acidic. For example, the pKa values for ethane, ethene, and acetylene are 51, 44, and 25, respectively, as shown here.
11.2K
Predicting Products: SN1 vs. SN202:27

Predicting Products: SN1 vs. SN2

17.3K
Nucleophilic substitution reactions of alkyl halides can proceed via an SN1 or an SN2 mechanism. While in SN2 reactions, the nucleophile attacks the substrate simultaneously as the leaving group departs, in SN1 reactions, the substrate first dissociates to give the carbocation intermediate. Various factors such as the structure of the substrate, the strength of the nucleophile, and the nature of the solvent promote one mechanism over the other.
With increased substitution on the alkyl halide,...
17.3K
Preparation of 1° Amines: Gabriel Synthesis01:28

Preparation of 1° Amines: Gabriel Synthesis

4.6K
Direct alkylation is not a suitable method for synthesizing amines because it produces polyalkylated products. Gabriel synthesis is the most preferred method to exclusively make primary amines. The method uses phthalimide, which contains a protected form of nitrogen that participates in alkylation only once to predominantly give primary amines.
Strong bases like NaOH or KOH deprotonate the phthalimide to form the corresponding anion, which acts as a nucleophile. Further, the anion attacks an...
4.6K

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Related Experiment Video

Updated: Jan 30, 2026

Growing Magnetotactic Bacteria of the Genus Magnetospirillum: Strains MSR-1, AMB-1 and MS-1
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Polyquaternium-1-Associated Dendritiform Keratopathy.

Angela Verkade1, Alice Y Matoba

  • 1Department of Ophthalmology, Baylor College of Medicine, Houston, TX.

Cornea
|February 1, 2019
PubMed
Summary
This summary is machine-generated.

Polyquaternium-1 (PQ-1) in eye drops can cause dendritiform keratopathy, even in patients who previously tolerated it. This condition may be dose-dependent, suggesting toxicity rather than hypersensitivity.

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Area of Science:

  • Ophthalmology
  • Corneal Disease
  • Ocular Surface Disease

Background:

  • Artificial tears are widely used for dry eye disease.
  • Preservatives in artificial tears can cause ocular surface toxicity.
  • Polyquaternium-1 (PQ-1) is a common preservative in artificial tears.

Observation:

  • A case of dendritiform keratopathy developed in a patient using Systane artificial tears.
  • The patient's use of Systane increased significantly prior to symptom onset.
  • The corneal condition resolved upon discontinuation of the artificial tears.

Findings:

  • The patient developed polyquaternium-1-associated dendritiform keratopathy.
  • The onset and resolution of keratopathy appeared to be dose-dependent.
  • The mechanism is suggested to be toxicity rather than hypersensitivity.

Implications:

  • Ophthalmologists should consider preservative toxicity, specifically PQ-1, in cases of unexplained dendritiform keratopathy.
  • Patients previously tolerating a preservative may develop toxicity with increased usage.
  • Discontinuation of the offending agent is crucial for resolution.