Cis-trans and Markovnikov (exam)

Cis-trans and Markovnikov (exam)

What is it?

Cis-trans: two different groups on each C of C=C. But-2-ene yes; 2-methylbut-2-ene maybe not if one carbon has two methyls. Markovnikov: in HX addition to an unsymmetric alkene, H goes to the carbon already holding more hydrogens (the other carbon gets X). School reason: more stable carbocation if a two-step picture is taught. Meaning: name the major product in an exam. Cis same side on C=C; trans opposite — needs two different groups on each C. Show curly arrows on addition mechanisms; Markovnikov reasoning must precede the product structure.

In simple words

• Cis-trans: two different groups on each C of C=C.
• 1. CIS-TRANS: Ethene no (two H on each C).
• 2. MAJOR PRODUCT: Propene + HBr -> 2-bromopropane major.
• Exam reminder: Worked propene + HBr: H to the CH2 end (already two H) Br to the middle carbon major name: 2-bromopropane

Important terms

CIS-TRANS AND MARKOVNIKOV (EXAM): Cis-trans: two different groups on each C of C=C.

1. CIS-TRANS: Ethene no (two H on each C).

2. MAJOR PRODUCT: Propene + HBr -> 2-bromopropane major.

What you should learn

• Explain cis-trans and markovnikov (exam) in simple chemical language.
• Connect 1. cis-trans with 2. major product using equations, observations, or trends where needed.
• Answer a short Federal Board question with the correct terms and a clear reason.

Examples

• But-2-ene
• Maleic/fumaric named if asked
• No rotation

CIS-TRANS

Ethene no (two H on each C). Propene no (CH2 end has two H). But-2-ene yes. EZ named if the book uses CIP, else cis-trans is enough. Markovnikov: H adds to C with more H already (rich get richer) for HX addition.

MAJOR PRODUCT

Propene + HBr -> 2-bromopropane major. 1-bromopropane minor. Draw both if the paper asks. Not a synthesis of a solvent stock. Anti-Markovnikov with peroxide for HBr only — school exception named.

Full school-level explanation

Cis-trans: two different groups on each C of C=C. But-2-ene yes; 2-methylbut-2-ene maybe not if one carbon has two methyls. Markovnikov: in HX addition to an unsymmetric alkene, H goes to the carbon already holding more hydrogens (the other carbon gets X). School reason: more stable carbocation if a two-step picture is taught. Meaning: name the major product in an exam. Cis same side on C=C; trans opposite — needs two different groups on each C. Show curly arrows on addition mechanisms; Markovnikov reasoning must precede the product structure.

Who can be cis, then who gets H:

WHAT — CIS-TRANS AND MARKOVNIKOV (EXAM)

Cis-trans: two different groups on each C of C=C. But-2-ene yes; 2-methylbut-2-ene maybe not if one carbon has two methyls. Markovnikov: in HX addition to an unsymmetric alkene, H goes to the carbon already holding more hydrogens (the other carbon gets X). School reason: more stable carbocation if a two-step picture is taught. Meaning: name the major product in an exam. Cis same side on C=C; trans opposite — needs two different groups on each C. Show curly arrows on addition mechanisms; Markovnikov reasoning must precede the product structure.

WHY — Why this topic matters

CIS-TRANS AND MARKOVNIKOV (EXAM) is an independent FBISE learning unit because students must use its definitions, conditions, equations, or trends separately in explanations and calculations.

HOW — How it works

CIS-TRANS: Ethene no (two H on each C). Propene no (CH2 end has two H). But-2-ene yes. EZ named if the book uses CIP, else cis-trans is enough. Markovnikov: H adds to C with more H already (rich get richer) for HX addition. Examples: But-2-ene; Maleic/fumaric named if asked; No rotation. MAJOR PRODUCT: Propene + HBr -> 2-bromopropane major. 1-bromopropane minor. Draw both if the paper asks. Not a synthesis of a solvent stock. Anti-Markovnikov with peroxide for HBr only — school exception named. Examples: H to CH2; Br to middle; Carbocation reason if taught. Worked propene + HBr: H to the CH2 end (already two H) Br to the middle carbon major name: 2-bromopropane

CIS-TRANS

Ethene no (two H on each C). Propene no (CH2 end has two H). But-2-ene yes. EZ named if the book uses CIP, else cis-trans is enough. Markovnikov: H adds to C with more H already (rich get richer) for HX addition.

Remember

• check both carbons

Examples

• But-2-ene
• Maleic/fumaric named if asked
• No rotation

MAJOR PRODUCT

Propene + HBr -> 2-bromopropane major. 1-bromopropane minor. Draw both if the paper asks. Not a synthesis of a solvent stock. Anti-Markovnikov with peroxide for HBr only — school exception named.

Remember

• Markovnikov named

Examples

• H to CH2
• Br to middle
• Carbocation reason if taught

Remember

• cis-trans needs two different groups each C
• H to richer-H carbon
• 2-bromopropane
• names only
• check both carbons
• Markovnikov named
• cis-trans needs two different groups each C
• H to richer-H carbon

How the ideas connect

Worked propene + HBr: H to the CH2 end (already two H) Br to the middle carbon major name: 2-bromopropane

Deeper understanding

Go beyond memorising Cis-trans and Markovnikov (exam). Connect the definition to reasons, relationships, exceptions, and exam wording.

How the ideas connect

Worked propene + HBr: H to the CH2 end (already two H) Br to the middle carbon major name: 2-bromopropane

Common mistakes

Exam focus

Core Idea

1. CIS-TRANS

2. MAJOR PRODUCT

Exam Example

Exam focus

Quick revision

• cis-trans needs two different groups each C
• H to richer-H carbon
• 2-bromopropane
• names only
• CIS-TRANS AND MARKOVNIKOV (EXAM): Cis-trans: two different groups on each C of C=C.
• 1. CIS-TRANS: Ethene no (two H on each C).

Product names. No bulk HBr addition plant.

For long answers on Cis-trans and Markovnikov (exam): define clearly → explain the main parts → give one example → state one exam caution.