Chapter 11: Problem 20
What is the effect on the polarity of alkyl group in haloalkane after its reaction with metal?
Short Answer
Expert verified
The reaction with metal reduces or eliminates the polarity of the haloalkane's alkyl group.
Step by step solution
01
Understanding Polarity in Haloalkanes
Haloalkanes (also known as alkyl halides) contain an alkyl group and a halogen atom. Due to the difference in electronegativity between carbon and the halogen atom, the C-X bond (where X is a halogen) is polar, making the alkyl group seem partially positive.
02
Reaction with Metal: Sn2 Mechanism
When a haloalkane reacts with a metal, such as sodium, in a nucleophilic substitution reaction (often through the Sn2 mechanism), the halogen atom is replaced by the metal. This reaction often proceeds through the formation of a metal-alkyl intermediate.
03
Effect on Polarity: From Polar to Nonpolar
Once the halogen atom is replaced by the metal, the electron-withdrawing effect of the halogen is eliminated. The resulting compound may be significantly less polar or even nonpolar compared to the original haloalkane due to the introduction of the metal, which does not create a significant polar bond with the carbon.
04
Conclusion: Polarity Change
The net effect of the reaction with the metal is a reduction or elimination of polarity in the resulting compound. The alkyl group loses its partial positive charge as the polar bond to the halogen is replaced with a less polar metal-carbon bond.
Unlock Step-by-Step Solutions & Ace Your Exams!
-
Full Textbook Solutions
Get detailed explanations and key concepts
-
Unlimited Al creation
Al flashcards, explanations, exams and more...
-
Ads-free access
To over 500 millions flashcards
-
Money-back guarantee
We refund you if you fail your exam.
Over 30 million students worldwide already upgrade their learning with Vaia!
Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Chemical Polarity
Chemical polarity refers to the distribution of electrical charges over the atoms joined by the bond. In a covalent bond, electrons are shared between atoms, but they may not be shared equally. This unequal sharing is due to differences in electronegativity, a measure of an atom's ability to attract electrons to itself.
In haloalkanes, which are compounds consisting of an alkyl group bonded to a halogen, chemical polarity plays a significant role. The bond between carbon (part of the alkyl group) and a halogen atom is polar because halogens are usually more electronegative than carbon. This results in an uneven distribution of electron density, where the carbon is partially positive while the halogen becomes partially negative. Understanding this concept of polarity is crucial when studying the reactions of haloalkanes, as it influences their behavior and reactivity.
In haloalkanes, which are compounds consisting of an alkyl group bonded to a halogen, chemical polarity plays a significant role. The bond between carbon (part of the alkyl group) and a halogen atom is polar because halogens are usually more electronegative than carbon. This results in an uneven distribution of electron density, where the carbon is partially positive while the halogen becomes partially negative. Understanding this concept of polarity is crucial when studying the reactions of haloalkanes, as it influences their behavior and reactivity.
Nucleophilic Substitution
Nucleophilic substitution is a fundamental type of chemical reaction wherein a nucleophile, which is a chemical species with a pair of electrons to donate, replaces a leaving group in a molecule. This type of reaction is of paramount importance in organic chemistry because it allows for the modification and transformation of molecules.
In the context of haloalkanes, the halogen atom serves as the leaving group due to its higher electronegativity and resulting repulsion of electron pairs. When a strong nucleophile encounters a polar haloalkane, it attacks the electron-deficient carbon atom bonded to the halogen. This leads to the ejection of the halogen and the formation of a new bond with the nucleophile, creating a substituted product. Nucleophilic substitution reactions can proceed via different mechanisms, the most common of which are Sn1 and Sn2.
In the context of haloalkanes, the halogen atom serves as the leaving group due to its higher electronegativity and resulting repulsion of electron pairs. When a strong nucleophile encounters a polar haloalkane, it attacks the electron-deficient carbon atom bonded to the halogen. This leads to the ejection of the halogen and the formation of a new bond with the nucleophile, creating a substituted product. Nucleophilic substitution reactions can proceed via different mechanisms, the most common of which are Sn1 and Sn2.
Sn2 Mechanism
The Sn2 mechanism is one of the two main types of nucleophilic substitution reactions. "Sn2" stands for Substitution Nucleophilic Bimolecular. This mechanism is characterized by a single concerted step, meaning that bond breaking and bond forming occur simultaneously.
In an Sn2 reaction, the nucleophile attacks the carbon atom from the side opposite to where the leaving group (usually the halogen in haloalkanes) is bonded. This backside attack leads to an inversion of configuration at the carbon center. Sn2 reactions are typical of primary haloalkanes, where steric hindrance is minimal, allowing the nucleophile to approach the electrophilic carbon easily.
In an Sn2 reaction, the nucleophile attacks the carbon atom from the side opposite to where the leaving group (usually the halogen in haloalkanes) is bonded. This backside attack leads to an inversion of configuration at the carbon center. Sn2 reactions are typical of primary haloalkanes, where steric hindrance is minimal, allowing the nucleophile to approach the electrophilic carbon easily.
- Occurs in a single concerted step
- Involves a backside attack
- Leads to inversion of configuration
- Generally faster in less hindered (primary) haloalkanes
Alkyl Group Polarity
Alkyl group polarity is an important concept when discussing haloalkane reactions. The alkyl group itself is generally nonpolar because it consists of C-H bonds, which have similar electronegativities. However, when this group is connected to a more electronegative atom such as a halogen in haloalkanes, the polarity changes.
The introduction of a halogen atom to the alkyl group creates a polar C-X bond. Here, the term polarity refers to the creation of a partial positive charge on the carbon and a partial negative charge on the halogen. This change in polarity is pivotal for reactions such as nucleophilic substitution, where the polarity of the C-X bond makes the carbon atom electrophilic, or positively charged and thus attractive to nucleophiles. After the reaction with a metal, this polarity is often reduced, and in some cases, the alkyl group can become nonpolar again. Reducing polarity is crucial for changing the reactivity and properties of the molecule.
The introduction of a halogen atom to the alkyl group creates a polar C-X bond. Here, the term polarity refers to the creation of a partial positive charge on the carbon and a partial negative charge on the halogen. This change in polarity is pivotal for reactions such as nucleophilic substitution, where the polarity of the C-X bond makes the carbon atom electrophilic, or positively charged and thus attractive to nucleophiles. After the reaction with a metal, this polarity is often reduced, and in some cases, the alkyl group can become nonpolar again. Reducing polarity is crucial for changing the reactivity and properties of the molecule.
