Question

The compound having only primary hydrogen atoms is (a) isobutene (b) 2,3 -dimethyl but- 2 -ene (c) cyclohexane (d) propyne

Short answer

The compound with only primary hydrogen atoms is (d) propyne.

Step-by-step solution

Understanding Primary Hydrogen Atoms

A primary hydrogen atom is bonded to a primary carbon atom, which is a carbon connected to only one other carbon. Identify the structure that only contains such hydrogen atoms.

Analyzing Isobutene

Isobutene, or 2-methylpropene, has the formula C₄H₈. Look at its structure: \( CH_2=C(CH_3)_2 \). It has one methyl group which contains primary hydrogens, but the hydrogen on the double-bonded carbon is secondary. Hence, it does not have only primary hydrogen atoms.

Analyzing 2,3-Dimethylbut-2-ene

The structure of 2,3-dimethylbut-2-ene is \( (CH_3)_2C=C(CH_3)_2 \). Both ends of the double bond are connected to carbon atoms, resulting in secondary hydrogens. Thus, it does not consist solely of primary hydrogen atoms.

Analyzing Cyclohexane

Cyclohexane is a saturated hydrocarbon with the formula \( C_6H_{12} \). In its structure, all carbon atoms are bonded to two other carbon atoms and two hydrogen atoms. Therefore, each hydrogen is secondary, not primary.

Analyzing Propyne

Propyne is \( CH_3C riplebond C-H \). The \( CH_3 \) group is attached to only one other carbon, making its hydrogens primary. Since all hydrogens in propyne are in primary positions, it is the correct answer.

Key concepts

Primary Hydrogen Atoms

In organic chemistry, the concept of primary hydrogen atoms is vital when analyzing molecular structures. A primary hydrogen atom is one that is attached to a primary carbon atom. A primary carbon atom itself is connected to only one other carbon atom. This simple definition allows chemists to easily categorize and evaluate the hydrogen atoms within a compound.

When identifying primary hydrogens in a molecule, it's important to examine each hydrogen's connection. If it's bonded to a carbon that links to just one other carbon, it is considered primary. In the context of the original exercise, identifying which compounds contain only these types of hydrogen atoms can significantly simplify understanding their structure and reactivity. A practical example is propyne, where the hydrogen atoms attached to its terminal methyl group are all primary. This trait can greatly influence both the physical properties and chemical behavior of the compound.

Isomers

Isomers are fascinating and illustrate the versatility of organic compounds. These are molecules that have the same molecular formula but differ in the arrangement of atoms. The differences in configuration can lead to vastly different properties.

There are several types of isomers, such as structural isomers and stereoisomers. Structural isomers, like butane and isobutane, have completely different frameworks. In contrast, stereoisomers have the same bond order but differ in spatial orientation, crucial in concepts like chirality.

Understanding isomers is key for molecular design and drug development because tiny changes in structure can lead to significant variation in biological activity and properties. This knowledge aids chemists in predicting reaction outcomes and designing efficient synthesis pathways.

Hydrocarbons

Hydrocarbons form the foundation of organic chemistry. They consist entirely of hydrogen and carbon atoms. Depending on the types of bonds between the carbon atoms, hydrocarbons can be alkanes, alkenes, alkynes, or aromatic compounds.

- **Alkanes:** Saturated hydrocarbons with single bonds, such as cyclohexane. - **Alkenes:** Contain at least one carbon-carbon double bond, like isobutene. - **Alkynes:** Feature at least one carbon-carbon triple bond, as seen in propyne.
These categories dictate the chemical reactivity and physical properties of the hydrocarbons. Each type has its characteristic reactions and utilities, making hydrocarbons central to both industrial and biological chemical processes.

Chemical Bonding

Chemical bonding describes the connection between atoms that enables them to form molecules. In hydrocarbons, different types of bonds can significantly impact the structure and behavior of the compound.

- **Single Bonds (σ-bonds):** Found in alkanes, allowing for free rotation around the bond axis. - **Double Bonds (π-bonds):** Present in alkenes, preventing rotation and creating a planar configuration. - **Triple Bonds:** Found in alkynes, such as propyne, which are linear and significantly stronger than double or single bonds. This increased strength can influence a compound’s stability and reactivity.
Understanding these types of bonding is crucial because they determine the molecule's geometry, physical properties, and how it will interact with other molecules.

Molecular Structure Analysis

Molecular structure analysis is like a molecular detective's work. It involves examining the three-dimensional arrangement of atoms within a molecule. This analysis is crucial in predicting both the physical and chemical properties of a substance.

Various techniques such as X-ray crystallography, NMR spectroscopy, and mass spectrometry are employed to determine structural details. By understanding the connectivity and geometry of atoms in a molecule, chemists can predict reactivity patterns, physical properties, and potential interactions with other molecules.

In the exercise, structure analysis helps identify primary hydrogens and differentiate between isomers. Recognizing structural aspects aids in understanding how changes in atoms or bonds can influence overall molecular behavior, enhancing synthetic strategies and applications in pharmaceuticals and materials science.