Reactivity 3.4 — SL Flashcards
What defines a nucleophile in chemical reactions?
A nucleophile is an electron-rich species (neutral molecule or negatively charged ion) that tends to donate a pair of non-bonding electrons to an electron-deficient species, forming a new covalent bond.
How does the reaction between bromoethane and hydroxide ion demonstrate nucleophilic substitution?
The hydroxide ion donates a pair of non-bonding electrons to the partially positively charged carbon atom in bromoethane, resulting in the formation of ethanol and bromide ion.
What role do “curly arrows” play in illustrating nucleophilic substitution reactions?
Curly arrows are used to show the movement of electron pairs during the reaction, indicating how bonds are broken and formed. The tail shows the source, and the head points to the destination of the electron pair.
Which common nucleophiles are used in organic chemistry reactions?
Neutral molecules with a lone pair of electrons, such as water (H2O) and ammonia (NH3), and negatively charged ions with a lone pair of electrons, such as halides (Cl−, Br−, I−), hydroxide (OH−), and cyanide (CN−).
Explain the significance of the reaction between bromoethane and the cyanide ion in demonstrating nucleophilic substitution.
This reaction showcases how the lone pair of electrons on the cyanide ion acts as a nucleophile, approaching the partially positively charged carbon atom in bromoethane, breaking the carbon-bromine bond, and forming a new bond between carbon and nitrogen, resulting in ethanenitrile and a bromide ion.
What is heterolytic fission and how does it differ from homolytic fission?
Heterolytic fission involves the breaking of a covalent bond with both electrons being taken by one atom, forming an anion and a cation. This contrasts with homolytic fission, where each atom receives one electron, forming two radicals.
Explain the role of heterolytic fission in nucleophilic substitution reactions.
Heterolytic fission facilitates nucleophilic substitution reactions by creating a positively charged site that attracts a nucleophile, leading to the substitution of the leaving group with the nucleophile.
How does the electronegativity of atoms affect heterolytic fission?
Electronegativity influences heterolytic fission by determining which atom retains the electron pair; the more electronegative atom attracts the electrons, becoming negatively charged, while the less electronegative atom becomes positively charged.
Give an example of heterolytic fission in a chemical reaction.
In the reaction between chloropropane and a hydroxide ion, heterolytic fission occurs when the bond between carbon and chlorine breaks, resulting in a carbocation and a chlorine ion.
What visual aid is used to illustrate the movement of electrons in heterolytic fission?
Curly arrows are used to show the direction of electron pair movement in heterolytic fission, indicating the transfer of electrons to one atom and the formation of ions.
What characterizes an electrophile in chemical reactions?
An electrophile is an electron-deficient species (neutral or positively charged atom) that tends to accept or attract a pair of electrons from a high electron density region, often initiating electrophilic addition or substitution reactions.
How does the electrophilic addition reaction occur between ethene and hydrogen bromide?
Hydrogen bromide, acting as an electrophile, is attracted to the electron-rich double bond of ethene, causing the bond to break. The hydrogen atom then attaches to one of the carbon atoms, while the bromine attaches to the other, forming 1-bromopropane.
What are common electrophiles used in electrophilic addition reactions?
Common electrophiles include protons (H+), carbocations, halogen molecules, hydrogen halides, and any molecule with a carbonyl group or atoms having incomplete octets like boron trifluoride.
Explain the electrophilic addition reaction mechanism of alkenes with halogens.
In the reaction between an alkene and a halogen, the high electron density of the alkene’s double bond attracts the halogen. The addition of the halogen across the double bond results in a vicinal dihalide, demonstrating the susceptibility of alkenes to electrophilic attack due to their electron-rich double bonds.
Describe the hydration reaction of alkenes and its significance.
Alkenes react with water in the presence of a catalyst like concentrated sulfuric acid to form alcohols in a hydration reaction. This reaction is significant for converting unsaturated hydrocarbons into useful alcohols like ethanol, which is important in industries and laboratories.
