Learning Arc 01 · Read and classify carbon-halogen structures
Build a Board-level systematic name
A name is useful only when another student can rebuild exactly the same atom connections and bond orders from it.
Foundation for this Concept6 symbols · 1 recovery lessons · 6 entry checksOpen
Start here: words and symbols used in this Concept
Open only the recovery material you need before the Mystery.
Read these words and symbols first
- IUPAC systematic name
- IUPAC means International Union of Pure and Applied Chemistry.
- A systematic name is a rule-built instruction for reconstructing one structure.
- This Concept covers only the open-chain, no-ring cases listed here.
- It does not teach every possible chemical name.
- open-chain or acyclic
- The connected carbon framework has no closed carbon loop.
- A ring is not open-chain.
- saturated parent
- Every carbon-carbon bond in the carbon path being tested is single.
- Apply this description only to the carbon path being tested.
- alkene
- The carbon path being tested contains a carbon-carbon double bond, C=C.
- Find the visible C=C before using the name ending ene.
- alkyne
- The carbon path being tested contains a carbon-carbon triple bond, C≡C.
- Find the visible C≡C before using the name ending yne.
- eligible parent path
- A continuous carbon path that contains the taught C=C or C≡C when one is present.
- Among eligible paths in this lesson, choose the longest.
Foundation 1
The name has a job
A systematic name is a fixed set of instructions for rebuilding one structure.
Do
Before naming, reconstruct every carbon, halogen and bond order in the displayed structure.
Entry check 1
List the non-hydrogen bonds in the displayed three-carbon structure and say whether C1/C2 labels are already finished-name position numbers.
Show the recovery
- C1-C2, C2-C3 and C2-Cl
- temporary analysis labels do not automatically become position numbers in the finished name.
Read each bond by endpoints, then keep analysis labels separate from the later numbering decision.
Entry check 2
What does CH3CH(Cl)CH3 say about the local attachment and hidden H?
Show the recovery
- Cl is attached to the middle CH
- the two terminal groups are CH3.
Expand the sequence and attach the bracketed group locally before counting H.
Entry check 3
In C=C and C≡C, what bond-order totals do the printed multiple bonds contribute?
Show the recovery
2 and 3.
Use the bond-order ledger: single 1, double 2, triple 3.
Entry check 4
In the skeletal diagnostic, how many carbon positions are implied, and what is the printed Br endpoint?
Show the recovery
- Four carbon positions are implied
- Br is bromine, not another carbon.
- Count an unlabelled line end, corner or branch junction as carbon
- a printed element symbol names that element.
Entry check 5
What must remain unchanged when a structure is redrawn?
Show the recovery
Atom inventory, every direct-neighbour pair and every bond order within this lesson's boundary.
Build the two bond ledgers and compare them, not the page shape.
Entry check 6
After ordinary carbon valency restores the hidden H atoms, what does a molecular formula record?
Show the recovery
- It records the total number of each element in one molecule
- it does not replace the bond map.
Complete each ordinary carbon to bond-order total four, total each element, and keep that inventory separate from connectivity.
1 · ObjectiveOpen
What you will understand
Choose, number and name the parent chain and halogen substituents required in this Chapter.
Problems this Concept unlocks
- name neutral open-chain (no-ring) halogen derivatives for Maharashtra HSC
- move from a systematic name back to a verified structure
- handle simple methyl or ethyl branches and one C=C or C≡C case required by the NCERT extension
2 · MysteryOpen
The problem to explain
Read these words and symbols first
- IUPAC systematic name
- IUPAC means International Union of Pure and Applied Chemistry.
- A systematic name is a rule-built instruction for reconstructing one structure.
- This Concept covers only the open-chain, no-ring cases listed here.
- It does not teach every possible chemical name.
- The displayed structure has three connected carbons and chlorine on the middle carbon.
- Munna proposes the incomplete name chloropropane.
Could another student rebuild the exact structure from chloropropane alone, or is one position instruction missing?
Your decision
State which structural fact the proposed name fails to locate before opening Learn.
3 · InvestigationOpen
Investigation
Investigation 1
Choose the parent before numbering
Read these words and symbols first
- parent chain
- The selected continuous carbon path that supplies the main name.
- A parent is a connected path, not simply the row that looks longest on the page.
- open-chain or acyclic
- The connected carbon framework has no closed carbon loop.
- A ring is not open-chain.
- eligible parent path
- A continuous carbon path that contains the taught C=C or C≡C when one is present.
- Among eligible paths in this lesson, choose the longest.
- alkene
- The carbon path being tested contains a carbon-carbon double bond, C=C.
- Find the visible C=C before using the name ending ene.
- alkyne
- The carbon path being tested contains a carbon-carbon triple bond, C≡C.
- Find the visible C≡C before using the name ending yne.
Do
- Trace each possible connected carbon path.
- Then apply the four checks in order.
Check
The mystery structure has one three-carbon parent path.
Investigation 2
Encode parent size and bond type
Read these words and symbols first
- carbon root
- meth, eth, prop, but, pent or hex records one to six parent carbons.
- Count only parent carbons, not every carbon in branches.
- parent ending
- ane, ene or yne records only single C-C bonds, one C=C, or one C≡C in this bounded lesson.
- The position of ene or yne must also be recorded.
Do
Count parent carbons, then inspect parent C-C bond orders.
Check
Three parent carbons with only C-C single bonds give propane.
Investigation 3
Assign locants from a chosen end
Read these words and symbols first
- locant
- A position number assigned after the parent is selected and numbered.
- It is not a temporary analysis label printed before the naming decision.
Do
Number the same parent from both ends and write both candidate position lists.
Check
The middle carbon is locant 2 from either end.
Investigation 4
Name what remains outside the parent
Read these words and symbols first
- substituent
- An atom or group shown in place of one H on the chosen parent structure.
- Cl in CH3-CH2-Cl is a substituent on the two-carbon parent.
- A carbon already inside the parent chain is not named again as a substituent.
- prefix
- fluoro, chloro, bromo or iodo names the attached halogen before the parent name.
- The prefix needs a locant when position could differ.
- methyl or ethyl branch
- A one-carbon or two-carbon branch left after the parent is selected.
- Do not call a path a branch until the parent decision is complete.
Do
- Mark parent atoms first
- classify every remaining directly attached group.
Check
The mystery's only non-parent group is chloro at locant 2.
Investigation 5
Choose between the two directions
Read these words and symbols first
- parent ending
- ane, ene or yne records only single C-C bonds, one C=C, or one C≡C in this bounded lesson.
- The position of ene or yne must also be recorded.
- locant
- A position number assigned after the parent is selected and numbered.
- It is not a temporary analysis label printed before the naming decision.
- ordered locant sequence
- The full sorted position list compared at the first point where two numbering directions differ.
- Do not choose by adding the locants.
Do
- Write both candidate sequences side by side.
- Circle the first unequal entry.
Check
- Mixed-halogen propane: compare 1,2 with 2,3.
- The first entries are 1 and 2.
- Therefore 1,2 wins.
Investigation 6
Record repeats, then order different prefixes
Read these words and symbols first
- di, tri, tetra
- Prefixes for two, three or four identical substituents.
- Every locant is still written
- these prefixes are ignored during alphabetising.
- alphabetical prefix order
- After numbering is fixed, different substituent roots are written alphabetically.
- It resolves numbering only in the bounded exact-tie case after all earlier comparisons tie.
Do
- Build one row for each substituent root.
- Then assemble the name.
Check
- Br at 1 and 2 becomes 1,2-dibromo.
- For Cl-CH2-CH2-Br, both directions give 1,2.
- Only then does bromo receive locant 1.
Investigation 7
Assemble one readable instruction
Read these words and symbols first
- name punctuation
- Commas separate numbers
- hyphens separate numbers and words
- one name has no spaces.
- Punctuation carries structure and is not decoration.
Do
Read the name token by token: locants, prefix, then parent.
Check
1,2-dibromoethane has a comma between 1 and 2 and a hyphen before dibromo.
Investigation 8
Prove the name by rebuilding
Read these words and symbols first
- name-to-graph check
- Rebuild the structure from the completed name and compare the two graphs.
- Matching molecular formulas alone is not enough.
Do
Create a fresh non-hydrogen bond ledger from the name without looking at the source ledger.
Check
2-chloropropane rebuilds a three-carbon chain with C2-Cl.
4 · MeaningOpen
Build the meaning
Meaning 1
Choose the parent before numbering
- Trace continuous carbon paths without jumping across a branch.
- If C=C or C≡C is present, keep only paths containing it.
- Choose the longest remaining path.
- That path is the parent.
Check
The mystery structure has one three-carbon parent path.
Meaning 2
Encode parent size and bond type
- Use meth, eth, prop, but, pent or hex for one to six parent carbons
- use ane, ene or yne for all-single, one-double or one-triple-bond cases taught here.
Check
Three parent carbons with only C-C single bonds give propane.
Meaning 3
Assign locants from a chosen end
- A locant is a position number produced by numbering the selected parent
- temporary C labels used to inspect a drawing do not decide the locants.
Check
The middle carbon is locant 2 from either end.
Meaning 4
Name what remains outside the parent
- Use fluoro, chloro, bromo or iodo for a halogen
- after the parent is fixed, use methyl or ethyl for a one- or two-carbon branch.
Check
The mystery's only non-parent group is chloro at locant 2.
Meaning 5
Choose between the two directions
- For C=C or C≡C, its locant is the smaller number on its two parent carbons.
- First lower the multiple-bond locant.
- If tied, or if no multiple bond exists, compare the ordered substituent locants.
- Stop at the first unequal locant.
- If every locant ties, use the bounded tie rule in the next step.
Check
- Mixed-halogen propane: compare 1,2 with 2,3.
- The first entries are 1 and 2.
- Therefore 1,2 wins.
Meaning 6
Record repeats, then order different prefixes
- Use di, tri or tetra for identical substituents.
- Keep every locant.
- Fix numbering before arranging prefix words.
- Write different prefix roots alphabetically.
- Ignore di, tri and tetra while alphabetising.
- Use the alphabetic tie rule only when every earlier numbering comparison ties.
Check
- Br at 1 and 2 becomes 1,2-dibromo.
- For Cl-CH2-CH2-Br, both directions give 1,2.
- Only then does bromo receive locant 1.
Meaning 7
Assemble one readable instruction
Use commas between numbers, hyphens between numbers and words, and no spaces inside a systematic name.
Check
1,2-dibromoethane has a comma between 1 and 2 and a hyphen before dibromo.
Meaning 8
Prove the name by rebuilding
- Rebuild the parent, bond orders and each located substituent from the finished name
- then compare atom inventory, direct-neighbour pairs and bond order with the source.
Check
2-chloropropane rebuilds a three-carbon chain with C2-Cl.
5 · ExamplesOpen
Worked examples
Example 1 of 4
Separate numbering from word order
Name the three-carbon Br/Cl structure.
Key evidence
- Three-carbon saturated parent
- Candidate locant sequences 1,2 and 2,3
- bromo alphabetically precedes chloro
One lawful move at a time
One move at a time
Step 1 of 3
- Action
- Choose propane
- Why
- Three continuous carbons and only single C-C bonds
- Result
- propane
Answer
2-bromo-1-chloropropane
Independent check
The name rebuilds C2-Br and C1-Cl on propane.
Counter-pattern
The lower locant 1 does not force chloro to be written before bromo.
6 · QuestionsOpen
Questions
Question 1 of 12
Read a systematic name as ordered reconstruction instructions.
Match each part of 1-chloropropane to its structural instruction.
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